diff --git a/googlemock/docs/cheat_sheet.md b/googlemock/docs/cheat_sheet.md
index 618c62d..850963a 100644
--- a/googlemock/docs/cheat_sheet.md
+++ b/googlemock/docs/cheat_sheet.md
@@ -742,12 +742,12 @@
 using ::testing::Mock;
 ...
 // Verifies and removes the expectations on mock_obj;
-// returns true if successful.
+// returns true if and only if successful.
 Mock::VerifyAndClearExpectations(&mock_obj);
 ...
 // Verifies and removes the expectations on mock_obj;
 // also removes the default actions set by ON_CALL();
-// returns true if successful.
+// returns true if and only if successful.
 Mock::VerifyAndClear(&mock_obj);
 ```
 
diff --git a/googlemock/docs/cook_book.md b/googlemock/docs/cook_book.md
index 28f7ba1..3a3308e 100644
--- a/googlemock/docs/cook_book.md
+++ b/googlemock/docs/cook_book.md
@@ -1270,8 +1270,8 @@
 the pointer itself, has a certain property? Well, you can use the `Pointee(m)`
 matcher.
 
-`Pointee(m)` matches a pointer if `m` matches the value the pointer points to.
-For example:
+`Pointee(m)` matches a pointer if and only if `m` matches the value the pointer
+points to. For example:
 
 ```cpp
 using ::testing::Ge;
@@ -3573,7 +3573,7 @@
  public:
   virtual ~MatcherInterface();
 
-  // Returns true if the matcher matches x; also explains the match
+  // Returns true if and only if the matcher matches x; also explains the match
   // result to 'listener'.
   virtual bool MatchAndExplain(T x, MatchResultListener* listener) const = 0;
 
@@ -3727,10 +3727,11 @@
  public:
   virtual ~CardinalityInterface();
 
-  // Returns true if call_count calls will satisfy this cardinality.
+  // Returns true if and only if call_count calls will satisfy this cardinality.
   virtual bool IsSatisfiedByCallCount(int call_count) const = 0;
 
-  // Returns true if call_count calls will saturate this cardinality.
+  // Returns true if and only if call_count calls will saturate this
+  // cardinality.
   virtual bool IsSaturatedByCallCount(int call_count) const = 0;
 
   // Describes self to an ostream.
diff --git a/googlemock/include/gmock/gmock-actions.h b/googlemock/include/gmock/gmock-actions.h
index 9842f32..f12d39b 100644
--- a/googlemock/include/gmock/gmock-actions.h
+++ b/googlemock/include/gmock/gmock-actions.h
@@ -99,7 +99,8 @@
 template <typename T>
 class BuiltInDefaultValue {
  public:
-  // This function returns true if type T has a built-in default value.
+  // This function returns true if and only if type T has a built-in default
+  // value.
   static bool Exists() {
     return ::std::is_default_constructible<T>::value;
   }
@@ -208,7 +209,7 @@
     producer_ = nullptr;
   }
 
-  // Returns true if the user has set the default value for type T.
+  // Returns true if and only if the user has set the default value for type T.
   static bool IsSet() { return producer_ != nullptr; }
 
   // Returns true if T has a default return value set by the user or there
@@ -269,7 +270,7 @@
   // Unsets the default value for type T&.
   static void Clear() { address_ = nullptr; }
 
-  // Returns true if the user has set the default value for type T&.
+  // Returns true if and only if the user has set the default value for type T&.
   static bool IsSet() { return address_ != nullptr; }
 
   // Returns true if T has a default return value set by the user or there
@@ -375,7 +376,7 @@
   template <typename Func>
   explicit Action(const Action<Func>& action) : fun_(action.fun_) {}
 
-  // Returns true if this is the DoDefault() action.
+  // Returns true if and only if this is the DoDefault() action.
   bool IsDoDefault() const { return fun_ == nullptr; }
 
   // Performs the action.  Note that this method is const even though
@@ -395,7 +396,7 @@
   template <typename G>
   friend class Action;
 
-  // fun_ is an empty function if this is the DoDefault() action.
+  // fun_ is an empty function if and only if this is the DoDefault() action.
   ::std::function<F> fun_;
 };
 
diff --git a/googlemock/include/gmock/gmock-cardinalities.h b/googlemock/include/gmock/gmock-cardinalities.h
index 4b269a3..46e01e1 100644
--- a/googlemock/include/gmock/gmock-cardinalities.h
+++ b/googlemock/include/gmock/gmock-cardinalities.h
@@ -70,10 +70,12 @@
   virtual int ConservativeLowerBound() const { return 0; }
   virtual int ConservativeUpperBound() const { return INT_MAX; }
 
-  // Returns true if call_count calls will satisfy this cardinality.
+  // Returns true if and only if call_count calls will satisfy this
+  // cardinality.
   virtual bool IsSatisfiedByCallCount(int call_count) const = 0;
 
-  // Returns true if call_count calls will saturate this cardinality.
+  // Returns true if and only if call_count calls will saturate this
+  // cardinality.
   virtual bool IsSaturatedByCallCount(int call_count) const = 0;
 
   // Describes self to an ostream.
@@ -98,17 +100,19 @@
   int ConservativeLowerBound() const { return impl_->ConservativeLowerBound(); }
   int ConservativeUpperBound() const { return impl_->ConservativeUpperBound(); }
 
-  // Returns true if call_count calls will satisfy this cardinality.
+  // Returns true if and only if call_count calls will satisfy this
+  // cardinality.
   bool IsSatisfiedByCallCount(int call_count) const {
     return impl_->IsSatisfiedByCallCount(call_count);
   }
 
-  // Returns true if call_count calls will saturate this cardinality.
+  // Returns true if and only if call_count calls will saturate this
+  // cardinality.
   bool IsSaturatedByCallCount(int call_count) const {
     return impl_->IsSaturatedByCallCount(call_count);
   }
 
-  // Returns true if call_count calls will over-saturate this
+  // Returns true if and only if call_count calls will over-saturate this
   // cardinality, i.e. exceed the maximum number of allowed calls.
   bool IsOverSaturatedByCallCount(int call_count) const {
     return impl_->IsSaturatedByCallCount(call_count) &&
diff --git a/googlemock/include/gmock/gmock-matchers.h b/googlemock/include/gmock/gmock-matchers.h
index 7009215..ad16687 100644
--- a/googlemock/include/gmock/gmock-matchers.h
+++ b/googlemock/include/gmock/gmock-matchers.h
@@ -358,8 +358,8 @@
 class TuplePrefix {
  public:
   // TuplePrefix<N>::Matches(matcher_tuple, value_tuple) returns true
-  // if the first N fields of matcher_tuple matches the first N
-  // fields of value_tuple, respectively.
+  // if and only if the first N fields of matcher_tuple matches
+  // the first N fields of value_tuple, respectively.
   template <typename MatcherTuple, typename ValueTuple>
   static bool Matches(const MatcherTuple& matcher_tuple,
                       const ValueTuple& value_tuple) {
@@ -417,8 +417,8 @@
                                      ::std::ostream* /* os */) {}
 };
 
-// TupleMatches(matcher_tuple, value_tuple) returns true if all
-// matchers in matcher_tuple match the corresponding fields in
+// TupleMatches(matcher_tuple, value_tuple) returns true if and only if
+// all matchers in matcher_tuple match the corresponding fields in
 // value_tuple.  It is a compiler error if matcher_tuple and
 // value_tuple have different number of fields or incompatible field
 // types.
@@ -2530,7 +2530,8 @@
           testing::SafeMatcherCast<const KeyType&>(inner_matcher)) {
   }
 
-  // Returns true if 'key_value.first' (the key) matches the inner matcher.
+  // Returns true if and only if 'key_value.first' (the key) matches the inner
+  // matcher.
   bool MatchAndExplain(PairType key_value,
                        MatchResultListener* listener) const override {
     StringMatchResultListener inner_listener;
@@ -2612,8 +2613,8 @@
     second_matcher_.DescribeNegationTo(os);
   }
 
-  // Returns true if 'a_pair.first' matches first_matcher and 'a_pair.second'
-  // matches second_matcher.
+  // Returns true if and only if 'a_pair.first' matches first_matcher and
+  // 'a_pair.second' matches second_matcher.
   bool MatchAndExplain(PairType a_pair,
                        MatchResultListener* listener) const override {
     if (!listener->IsInterested()) {
@@ -3148,8 +3149,8 @@
 
 // Given a 2-tuple matcher tm of type Tuple2Matcher and a value second
 // of type Second, BoundSecondMatcher<Tuple2Matcher, Second>(tm,
-// second) is a polymorphic matcher that matches a value x if tm
-// matches tuple (x, second).  Useful for implementing
+// second) is a polymorphic matcher that matches a value x if and only if
+// tm matches tuple (x, second).  Useful for implementing
 // UnorderedPointwise() in terms of UnorderedElementsAreArray().
 //
 // BoundSecondMatcher is copyable and assignable, as we need to put
@@ -3213,8 +3214,8 @@
 
 // Given a 2-tuple matcher tm and a value second,
 // MatcherBindSecond(tm, second) returns a matcher that matches a
-// value x if tm matches tuple (x, second).  Useful for implementing
-// UnorderedPointwise() in terms of UnorderedElementsAreArray().
+// value x if and only if tm matches tuple (x, second).  Useful for
+// implementing UnorderedPointwise() in terms of UnorderedElementsAreArray().
 template <typename Tuple2Matcher, typename Second>
 BoundSecondMatcher<Tuple2Matcher, Second> MatcherBindSecond(
     const Tuple2Matcher& tm, const Second& second) {
@@ -3705,7 +3706,7 @@
 // Creates a matcher that matches an object whose given field matches
 // 'matcher'.  For example,
 //   Field(&Foo::number, Ge(5))
-// matches a Foo object x if x.number >= 5.
+// matches a Foo object x if and only if x.number >= 5.
 template <typename Class, typename FieldType, typename FieldMatcher>
 inline PolymorphicMatcher<
   internal::FieldMatcher<Class, FieldType> > Field(
@@ -3732,7 +3733,7 @@
 // Creates a matcher that matches an object whose given property
 // matches 'matcher'.  For example,
 //   Property(&Foo::str, StartsWith("hi"))
-// matches a Foo object x if x.str() starts with "hi".
+// matches a Foo object x if and only if x.str() starts with "hi".
 template <typename Class, typename PropertyType, typename PropertyMatcher>
 inline PolymorphicMatcher<internal::PropertyMatcher<
     Class, PropertyType, PropertyType (Class::*)() const> >
@@ -3787,11 +3788,10 @@
           property_name, property, MatcherCast<const PropertyType&>(matcher)));
 }
 
-// Creates a matcher that matches an object if the result of applying
-// a callable to x matches 'matcher'.
-// For example,
+// Creates a matcher that matches an object if and only if the result of
+// applying a callable to x matches 'matcher'. For example,
 //   ResultOf(f, StartsWith("hi"))
-// matches a Foo object x if f(x) starts with "hi".
+// matches a Foo object x if and only if f(x) starts with "hi".
 // `callable` parameter can be a function, function pointer, or a functor. It is
 // required to keep no state affecting the results of the calls on it and make
 // no assumptions about how many calls will be made. Any state it keeps must be
@@ -4341,7 +4341,7 @@
   return internal::MatcherAsPredicate<M>(matcher);
 }
 
-// Returns true if the value matches the matcher.
+// Returns true if and only if the value matches the matcher.
 template <typename T, typename M>
 inline bool Value(const T& value, M matcher) {
   return testing::Matches(matcher)(value);
@@ -4547,8 +4547,8 @@
 
 // These macros allow using matchers to check values in Google Test
 // tests.  ASSERT_THAT(value, matcher) and EXPECT_THAT(value, matcher)
-// succeed if the value matches the matcher.  If the assertion fails,
-// the value and the description of the matcher will be printed.
+// succeed if and only if the value matches the matcher.  If the assertion
+// fails, the value and the description of the matcher will be printed.
 #define ASSERT_THAT(value, matcher) ASSERT_PRED_FORMAT1(\
     ::testing::internal::MakePredicateFormatterFromMatcher(matcher), value)
 #define EXPECT_THAT(value, matcher) EXPECT_PRED_FORMAT1(\
diff --git a/googlemock/include/gmock/gmock-spec-builders.h b/googlemock/include/gmock/gmock-spec-builders.h
index 66429df..80c13b5 100644
--- a/googlemock/include/gmock/gmock-spec-builders.h
+++ b/googlemock/include/gmock/gmock-spec-builders.h
@@ -332,7 +332,7 @@
     return *this;
   }
 
-  // Returns true if the given arguments match the matchers.
+  // Returns true if and only if the given arguments match the matchers.
   bool Matches(const ArgumentTuple& args) const {
     return TupleMatches(matchers_, args) && extra_matcher_.Matches(args);
   }
@@ -390,7 +390,7 @@
       GTEST_LOCK_EXCLUDED_(internal::g_gmock_mutex);
 
   // Verifies all expectations on the given mock object and clears its
-  // default actions and expectations.  Returns true if the
+  // default actions and expectations.  Returns true if and only if the
   // verification was successful.
   static bool VerifyAndClear(void* mock_obj)
       GTEST_LOCK_EXCLUDED_(internal::g_gmock_mutex);
@@ -516,7 +516,8 @@
   // The compiler-generated copy ctor and operator= work exactly as
   // intended, so we don't need to define our own.
 
-  // Returns true if rhs references the same expectation as this object does.
+  // Returns true if and only if rhs references the same expectation as this
+  // object does.
   bool operator==(const Expectation& rhs) const {
     return expectation_base_ == rhs.expectation_base_;
   }
@@ -598,8 +599,8 @@
   // The compiler-generator ctor and operator= works exactly as
   // intended, so we don't need to define our own.
 
-  // Returns true if rhs contains the same set of Expectation objects
-  // as this does.
+  // Returns true if and only if rhs contains the same set of Expectation
+  // objects as this does.
   bool operator==(const ExpectationSet& rhs) const {
     return expectations_ == rhs.expectations_;
   }
@@ -760,8 +761,8 @@
   // by the subclasses to implement the .Times() clause.
   void SpecifyCardinality(const Cardinality& cardinality);
 
-  // Returns true if the user specified the cardinality explicitly
-  // using a .Times().
+  // Returns true if and only if the user specified the cardinality
+  // explicitly using a .Times().
   bool cardinality_specified() const { return cardinality_specified_; }
 
   // Sets the cardinality of this expectation spec.
@@ -777,7 +778,7 @@
   void RetireAllPreRequisites()
       GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex);
 
-  // Returns true if this expectation is retired.
+  // Returns true if and only if this expectation is retired.
   bool is_retired() const
       GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex) {
     g_gmock_mutex.AssertHeld();
@@ -791,28 +792,29 @@
     retired_ = true;
   }
 
-  // Returns true if this expectation is satisfied.
+  // Returns true if and only if this expectation is satisfied.
   bool IsSatisfied() const
       GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex) {
     g_gmock_mutex.AssertHeld();
     return cardinality().IsSatisfiedByCallCount(call_count_);
   }
 
-  // Returns true if this expectation is saturated.
+  // Returns true if and only if this expectation is saturated.
   bool IsSaturated() const
       GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex) {
     g_gmock_mutex.AssertHeld();
     return cardinality().IsSaturatedByCallCount(call_count_);
   }
 
-  // Returns true if this expectation is over-saturated.
+  // Returns true if and only if this expectation is over-saturated.
   bool IsOverSaturated() const
       GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex) {
     g_gmock_mutex.AssertHeld();
     return cardinality().IsOverSaturatedByCallCount(call_count_);
   }
 
-  // Returns true if all pre-requisites of this expectation are satisfied.
+  // Returns true if and only if all pre-requisites of this expectation are
+  // satisfied.
   bool AllPrerequisitesAreSatisfied() const
       GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex);
 
@@ -855,7 +857,7 @@
   const char* file_;          // The file that contains the expectation.
   int line_;                  // The line number of the expectation.
   const std::string source_text_;  // The EXPECT_CALL(...) source text.
-  // True if the cardinality is specified explicitly.
+  // True if and only if the cardinality is specified explicitly.
   bool cardinality_specified_;
   Cardinality cardinality_;            // The cardinality of the expectation.
   // The immediate pre-requisites (i.e. expectations that must be
@@ -869,7 +871,7 @@
   // This group of fields are the current state of the expectation,
   // and can change as the mock function is called.
   int call_count_;  // How many times this expectation has been invoked.
-  bool retired_;    // True if this expectation has retired.
+  bool retired_;    // True if and only if this expectation has retired.
   UntypedActions untyped_actions_;
   bool extra_matcher_specified_;
   bool repeated_action_specified_;  // True if a WillRepeatedly() was specified.
@@ -1087,14 +1089,15 @@
   // statement finishes and when the current thread holds
   // g_gmock_mutex.
 
-  // Returns true if this expectation matches the given arguments.
+  // Returns true if and only if this expectation matches the given arguments.
   bool Matches(const ArgumentTuple& args) const
       GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex) {
     g_gmock_mutex.AssertHeld();
     return TupleMatches(matchers_, args) && extra_matcher_.Matches(args);
   }
 
-  // Returns true if this expectation should handle the given arguments.
+  // Returns true if and only if this expectation should handle the given
+  // arguments.
   bool ShouldHandleArguments(const ArgumentTuple& args) const
       GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex) {
     g_gmock_mutex.AssertHeld();
diff --git a/googlemock/include/gmock/internal/gmock-internal-utils.h b/googlemock/include/gmock/internal/gmock-internal-utils.h
index 53b6d97..e05b883 100644
--- a/googlemock/include/gmock/internal/gmock-internal-utils.h
+++ b/googlemock/include/gmock/internal/gmock-internal-utils.h
@@ -157,11 +157,11 @@
   static_cast< ::testing::internal::TypeKind>( \
       ::testing::internal::KindOf<type>::value)
 
-// Evaluates to true if integer type T is signed.
+// Evaluates to true if and only if integer type T is signed.
 #define GMOCK_IS_SIGNED_(T) (static_cast<T>(-1) < 0)
 
 // LosslessArithmeticConvertibleImpl<kFromKind, From, kToKind, To>::value
-// is true if arithmetic type From can be losslessly converted to
+// is true if and only if arithmetic type From can be losslessly converted to
 // arithmetic type To.
 //
 // It's the user's responsibility to ensure that both From and To are
@@ -192,8 +192,8 @@
 struct LosslessArithmeticConvertibleImpl<kInteger, From, kBool, bool>
     : public std::false_type {};
 
-// Converting an integer to another non-bool integer is lossless if
-// the target type's range encloses the source type's range.
+// Converting an integer to another non-bool integer is lossless
+// if and only if the target type's range encloses the source type's range.
 template <typename From, typename To>
 struct LosslessArithmeticConvertibleImpl<kInteger, From, kInteger, To>
     : public bool_constant<
@@ -224,14 +224,14 @@
     : public std::false_type {};
 
 // Converting a floating-point to another floating-point is lossless
-// if the target type is at least as big as the source type.
+// if and only if the target type is at least as big as the source type.
 template <typename From, typename To>
 struct LosslessArithmeticConvertibleImpl<
   kFloatingPoint, From, kFloatingPoint, To>
     : public bool_constant<sizeof(From) <= sizeof(To)> {};  // NOLINT
 
-// LosslessArithmeticConvertible<From, To>::value is true if arithmetic
-// type From can be losslessly converted to arithmetic type To.
+// LosslessArithmeticConvertible<From, To>::value is true if and only if
+// arithmetic type From can be losslessly converted to arithmetic type To.
 //
 // It's the user's responsibility to ensure that both From and To are
 // raw (i.e. has no CV modifier, is not a pointer, and is not a
@@ -305,11 +305,11 @@
 // No logs are printed.
 const char kErrorVerbosity[] = "error";
 
-// Returns true if a log with the given severity is visible according
-// to the --gmock_verbose flag.
+// Returns true if and only if a log with the given severity is visible
+// according to the --gmock_verbose flag.
 GTEST_API_ bool LogIsVisible(LogSeverity severity);
 
-// Prints the given message to stdout if 'severity' >= the level
+// Prints the given message to stdout if and only if 'severity' >= the level
 // specified by the --gmock_verbose flag.  If stack_frames_to_skip >=
 // 0, also prints the stack trace excluding the top
 // stack_frames_to_skip frames.  In opt mode, any positive
diff --git a/googlemock/src/gmock-internal-utils.cc b/googlemock/src/gmock-internal-utils.cc
index 1292e1d..e5b5479 100644
--- a/googlemock/src/gmock-internal-utils.cc
+++ b/googlemock/src/gmock-internal-utils.cc
@@ -123,8 +123,8 @@
 // Protects global resources (stdout in particular) used by Log().
 static GTEST_DEFINE_STATIC_MUTEX_(g_log_mutex);
 
-// Returns true if a log with the given severity is visible according
-// to the --gmock_verbose flag.
+// Returns true if and only if a log with the given severity is visible
+// according to the --gmock_verbose flag.
 GTEST_API_ bool LogIsVisible(LogSeverity severity) {
   if (GMOCK_FLAG(verbose) == kInfoVerbosity) {
     // Always show the log if --gmock_verbose=info.
@@ -139,7 +139,7 @@
   }
 }
 
-// Prints the given message to stdout if 'severity' >= the level
+// Prints the given message to stdout if and only if 'severity' >= the level
 // specified by the --gmock_verbose flag.  If stack_frames_to_skip >=
 // 0, also prints the stack trace excluding the top
 // stack_frames_to_skip frames.  In opt mode, any positive
diff --git a/googlemock/src/gmock-spec-builders.cc b/googlemock/src/gmock-spec-builders.cc
index f6705a3..f9d3434 100644
--- a/googlemock/src/gmock-spec-builders.cc
+++ b/googlemock/src/gmock-spec-builders.cc
@@ -126,8 +126,8 @@
   }
 }
 
-// Returns true if all pre-requisites of this expectation have been
-// satisfied.
+// Returns true if and only if all pre-requisites of this expectation
+// have been satisfied.
 bool ExpectationBase::AllPrerequisitesAreSatisfied() const
     GTEST_EXCLUSIVE_LOCK_REQUIRED_(g_gmock_mutex) {
   g_gmock_mutex.AssertHeld();
@@ -384,7 +384,7 @@
     const CallReaction reaction =
         Mock::GetReactionOnUninterestingCalls(MockObject());
 
-    // True if we need to print this call's arguments and return
+    // True if and only if we need to print this call's arguments and return
     // value.  This definition must be kept in sync with
     // the behavior of ReportUninterestingCall().
     const bool need_to_report_uninteresting_call =
@@ -435,7 +435,8 @@
           &ss, &why);
   const bool found = untyped_expectation != nullptr;
 
-  // True if we need to print the call's arguments and return value.
+  // True if and only if we need to print the call's arguments
+  // and return value.
   // This definition must be kept in sync with the uses of Expect()
   // and Log() in this function.
   const bool need_to_report_call =
@@ -574,7 +575,7 @@
   int first_used_line;
   ::std::string first_used_test_suite;
   ::std::string first_used_test;
-  bool leakable;  // true if it's OK to leak the object.
+  bool leakable;  // true if and only if it's OK to leak the object.
   FunctionMockers function_mockers;  // All registered methods of the object.
 };
 
@@ -718,7 +719,7 @@
 }
 
 // Verifies all expectations on the given mock object and clears its
-// default actions and expectations.  Returns true if the
+// default actions and expectations.  Returns true if and only if the
 // verification was successful.
 bool Mock::VerifyAndClear(void* mock_obj)
     GTEST_LOCK_EXCLUDED_(internal::g_gmock_mutex) {
diff --git a/googlemock/src/gmock.cc b/googlemock/src/gmock.cc
index ce926f2..32b2a73 100644
--- a/googlemock/src/gmock.cc
+++ b/googlemock/src/gmock.cc
@@ -34,8 +34,8 @@
 namespace testing {
 
 GMOCK_DEFINE_bool_(catch_leaked_mocks, true,
-                   "true if Google Mock should report leaked mock objects "
-                   "as failures.");
+                   "true if and only if Google Mock should report leaked "
+                   "mock objects as failures.");
 
 GMOCK_DEFINE_string_(verbose, internal::kWarningVerbosity,
                      "Controls how verbose Google Mock's output is."
diff --git a/googlemock/test/gmock-cardinalities_test.cc b/googlemock/test/gmock-cardinalities_test.cc
index 66042d4..ca97cae 100644
--- a/googlemock/test/gmock-cardinalities_test.cc
+++ b/googlemock/test/gmock-cardinalities_test.cc
@@ -395,12 +395,14 @@
 
 class EvenCardinality : public CardinalityInterface {
  public:
-  // Returns true if call_count calls will satisfy this cardinality.
+  // Returns true if and only if call_count calls will satisfy this
+  // cardinality.
   bool IsSatisfiedByCallCount(int call_count) const override {
     return (call_count % 2 == 0);
   }
 
-  // Returns true if call_count calls will saturate this cardinality.
+  // Returns true if and only if call_count calls will saturate this
+  // cardinality.
   bool IsSaturatedByCallCount(int /* call_count */) const override {
     return false;
   }
diff --git a/googlemock/test/gmock-matchers_test.cc b/googlemock/test/gmock-matchers_test.cc
index a61d040..88f144d 100644
--- a/googlemock/test/gmock-matchers_test.cc
+++ b/googlemock/test/gmock-matchers_test.cc
@@ -956,10 +956,9 @@
 
 // Tests that TypedEq<T>(v) has type Matcher<T>.
 
-// Type<T>::IsTypeOf(v) compiles if the type of value v is T, where T
-// is a "bare" type (i.e. not in the form of const U or U&).  If v's
-// type is not T, the compiler will generate a message about
-// "undefined reference".
+// Type<T>::IsTypeOf(v) compiles if and only if the type of value v is T, where
+// T is a "bare" type (i.e. not in the form of const U or U&).  If v's type is
+// not T, the compiler will generate a message about "undefined reference".
 template <typename T>
 struct Type {
   static bool IsTypeOf(const T& /* v */) { return true; }
@@ -2640,8 +2639,8 @@
 // For testing Truly().
 const int foo = 0;
 
-// This predicate returns true if the argument references foo and has
-// a zero value.
+// This predicate returns true if and only if the argument references foo and
+// has a zero value.
 bool ReferencesFooAndIsZero(const int& n) {
   return (&n == &foo) && (n == 0);
 }
@@ -3594,7 +3593,7 @@
   GTEST_DISALLOW_COPY_AND_ASSIGN_(Uncopyable);
 };
 
-// Returns true if x.value() is positive.
+// Returns true if and only if x.value() is positive.
 bool ValueIsPositive(const Uncopyable& x) { return x.value() > 0; }
 
 MATCHER_P(UncopyableIs, inner_matcher, "") {
diff --git a/googlemock/test/gmock-spec-builders_test.cc b/googlemock/test/gmock-spec-builders_test.cc
index 95b4b8b..7bf5a8a 100644
--- a/googlemock/test/gmock-spec-builders_test.cc
+++ b/googlemock/test/gmock-spec-builders_test.cc
@@ -1952,12 +1952,14 @@
 
 class EvenNumberCardinality : public CardinalityInterface {
  public:
-  // Returns true if call_count calls will satisfy this cardinality.
+  // Returns true if and only if call_count calls will satisfy this
+  // cardinality.
   bool IsSatisfiedByCallCount(int call_count) const override {
     return call_count % 2 == 0;
   }
 
-  // Returns true if call_count calls will saturate this cardinality.
+  // Returns true if and only if call_count calls will saturate this
+  // cardinality.
   bool IsSaturatedByCallCount(int /* call_count */) const override {
     return false;
   }
diff --git a/googletest/include/gtest/gtest-death-test.h b/googletest/include/gtest/gtest-death-test.h
index cec9629..dc878ff 100644
--- a/googletest/include/gtest/gtest-death-test.h
+++ b/googletest/include/gtest/gtest-death-test.h
@@ -276,20 +276,20 @@
 // This macro is used for implementing macros such as
 // EXPECT_DEATH_IF_SUPPORTED and ASSERT_DEATH_IF_SUPPORTED on systems where
 // death tests are not supported. Those macros must compile on such systems
-// if EXPECT_DEATH and ASSERT_DEATH compile with the same parameters on
-// systems that support death tests. This allows one to write such a macro
-// on a system that does not support death tests and be sure that it will
-// compile on a death-test supporting system. It is exposed publicly so that
-// systems that have death-tests with stricter requirements than
-// GTEST_HAS_DEATH_TEST can write their own equivalent of
-// EXPECT_DEATH_IF_SUPPORTED and ASSERT_DEATH_IF_SUPPORTED.
+// if and only if EXPECT_DEATH and ASSERT_DEATH compile with the same parameters
+// on systems that support death tests. This allows one to write such a macro on
+// a system that does not support death tests and be sure that it will compile
+// on a death-test supporting system. It is exposed publicly so that systems
+// that have death-tests with stricter requirements than GTEST_HAS_DEATH_TEST
+// can write their own equivalent of EXPECT_DEATH_IF_SUPPORTED and
+// ASSERT_DEATH_IF_SUPPORTED.
 //
 // Parameters:
 //   statement -  A statement that a macro such as EXPECT_DEATH would test
 //                for program termination. This macro has to make sure this
 //                statement is compiled but not executed, to ensure that
 //                EXPECT_DEATH_IF_SUPPORTED compiles with a certain
-//                parameter if EXPECT_DEATH compiles with it.
+//                parameter if and only if EXPECT_DEATH compiles with it.
 //   regex     -  A regex that a macro such as EXPECT_DEATH would use to test
 //                the output of statement.  This parameter has to be
 //                compiled but not evaluated by this macro, to ensure that
diff --git a/googletest/include/gtest/gtest-matchers.h b/googletest/include/gtest/gtest-matchers.h
index c10d650..9de6c2e 100644
--- a/googletest/include/gtest/gtest-matchers.h
+++ b/googletest/include/gtest/gtest-matchers.h
@@ -96,8 +96,8 @@
   // Returns the underlying ostream.
   ::std::ostream* stream() { return stream_; }
 
-  // Returns true if the listener is interested in an explanation of
-  // the match result.  A matcher's MatchAndExplain() method can use
+  // Returns true if and only if the listener is interested in an explanation
+  // of the match result.  A matcher's MatchAndExplain() method can use
   // this information to avoid generating the explanation when no one
   // intends to hear it.
   bool IsInterested() const { return stream_ != nullptr; }
@@ -141,8 +141,8 @@
 template <typename T>
 class MatcherInterface : public MatcherDescriberInterface {
  public:
-  // Returns true if the matcher matches x; also explains the match
-  // result to 'listener' if necessary (see the next paragraph), in
+  // Returns true if and only if the matcher matches x; also explains the
+  // match result to 'listener' if necessary (see the next paragraph), in
   // the form of a non-restrictive relative clause ("which ...",
   // "whose ...", etc) that describes x.  For example, the
   // MatchAndExplain() method of the Pointee(...) matcher should
@@ -258,13 +258,13 @@
 template <typename T>
 class MatcherBase {
  public:
-  // Returns true if the matcher matches x; also explains the match
-  // result to 'listener'.
+  // Returns true if and only if the matcher matches x; also explains the
+  // match result to 'listener'.
   bool MatchAndExplain(const T& x, MatchResultListener* listener) const {
     return impl_->MatchAndExplain(x, listener);
   }
 
-  // Returns true if this matcher matches x.
+  // Returns true if and only if this matcher matches x.
   bool Matches(const T& x) const {
     DummyMatchResultListener dummy;
     return MatchAndExplain(x, &dummy);
diff --git a/googletest/include/gtest/gtest-test-part.h b/googletest/include/gtest/gtest-test-part.h
index 4f189b6..05a7985 100644
--- a/googletest/include/gtest/gtest-test-part.h
+++ b/googletest/include/gtest/gtest-test-part.h
@@ -87,19 +87,19 @@
   // Gets the message associated with the test part.
   const char* message() const { return message_.c_str(); }
 
-  // Returns true if the test part was skipped.
+  // Returns true if and only if the test part was skipped.
   bool skipped() const { return type_ == kSkip; }
 
-  // Returns true if the test part passed.
+  // Returns true if and only if the test part passed.
   bool passed() const { return type_ == kSuccess; }
 
-  // Returns true if the test part non-fatally failed.
+  // Returns true if and only if the test part non-fatally failed.
   bool nonfatally_failed() const { return type_ == kNonFatalFailure; }
 
-  // Returns true if the test part fatally failed.
+  // Returns true if and only if the test part fatally failed.
   bool fatally_failed() const { return type_ == kFatalFailure; }
 
-  // Returns true if the test part failed.
+  // Returns true if and only if the test part failed.
   bool failed() const { return fatally_failed() || nonfatally_failed(); }
 
  private:
diff --git a/googletest/include/gtest/gtest.h b/googletest/include/gtest/gtest.h
index dfe7c78..8e125a4 100644
--- a/googletest/include/gtest/gtest.h
+++ b/googletest/include/gtest/gtest.h
@@ -308,7 +308,7 @@
     return *this;
   }
 
-  // Returns true if the assertion succeeded.
+  // Returns true if and only if the assertion succeeded.
   operator bool() const { return success_; }  // NOLINT
 
   // Returns the assertion's negation. Used with EXPECT/ASSERT_FALSE.
@@ -432,16 +432,16 @@
   static void SetUpTestCase() {}
 #endif  // GTEST_REMOVE_LEGACY_TEST_CASEAPI_
 
-  // Returns true if the current test has a fatal failure.
+  // Returns true if and only if the current test has a fatal failure.
   static bool HasFatalFailure();
 
-  // Returns true if the current test has a non-fatal failure.
+  // Returns true if and only if the current test has a non-fatal failure.
   static bool HasNonfatalFailure();
 
-  // Returns true if the current test was skipped.
+  // Returns true if and only if the current test was skipped.
   static bool IsSkipped();
 
-  // Returns true if the current test has a (either fatal or
+  // Returns true if and only if the current test has a (either fatal or
   // non-fatal) failure.
   static bool HasFailure() { return HasFatalFailure() || HasNonfatalFailure(); }
 
@@ -472,8 +472,8 @@
   virtual void TearDown();
 
  private:
-  // Returns true if the current test has the same fixture class as
-  // the first test in the current test suite.
+  // Returns true if and only if the current test has the same fixture class
+  // as the first test in the current test suite.
   static bool HasSameFixtureClass();
 
   // Runs the test after the test fixture has been set up.
@@ -574,19 +574,19 @@
   // Returns the number of the test properties.
   int test_property_count() const;
 
-  // Returns true if the test passed (i.e. no test part failed).
+  // Returns true if and only if the test passed (i.e. no test part failed).
   bool Passed() const { return !Skipped() && !Failed(); }
 
-  // Returns true if the test was skipped.
+  // Returns true if and only if the test was skipped.
   bool Skipped() const;
 
-  // Returns true if the test failed.
+  // Returns true if and only if the test failed.
   bool Failed() const;
 
-  // Returns true if the test fatally failed.
+  // Returns true if and only if the test fatally failed.
   bool HasFatalFailure() const;
 
-  // Returns true if the test has a non-fatal failure.
+  // Returns true if and only if the test has a non-fatal failure.
   bool HasNonfatalFailure() const;
 
   // Returns the elapsed time, in milliseconds.
@@ -750,7 +750,7 @@
   // contains the character 'A' or starts with "Foo.".
   bool should_run() const { return should_run_; }
 
-  // Returns true if this test will appear in the XML report.
+  // Returns true if and only if this test will appear in the XML report.
   bool is_reportable() const {
     // The XML report includes tests matching the filter, excluding those
     // run in other shards.
@@ -808,12 +808,12 @@
   // value-parameterized test.
   const std::unique_ptr<const ::std::string> value_param_;
   internal::CodeLocation location_;
-  const internal::TypeId fixture_class_id_;   // ID of the test fixture class
-  bool should_run_;                 // True if this test should run
-  bool is_disabled_;                // True if this test is disabled
-  bool matches_filter_;             // True if this test matches the
-                                    // user-specified filter.
-  bool is_in_another_shard_;        // Will be run in another shard.
+  const internal::TypeId fixture_class_id_;  // ID of the test fixture class
+  bool should_run_;           // True if and only if this test should run
+  bool is_disabled_;          // True if and only if this test is disabled
+  bool matches_filter_;       // True if this test matches the
+                              // user-specified filter.
+  bool is_in_another_shard_;  // Will be run in another shard.
   internal::TestFactoryBase* const factory_;  // The factory that creates
                                               // the test object
 
@@ -885,10 +885,10 @@
   // Gets the number of all tests in this test suite.
   int total_test_count() const;
 
-  // Returns true if the test suite passed.
+  // Returns true if and only if the test suite passed.
   bool Passed() const { return !Failed(); }
 
-  // Returns true if the test suite failed.
+  // Returns true if and only if the test suite failed.
   bool Failed() const { return failed_test_count() > 0; }
 
   // Returns the elapsed time, in milliseconds.
@@ -956,33 +956,33 @@
     }
   }
 
-  // Returns true if test passed.
+  // Returns true if and only if test passed.
   static bool TestPassed(const TestInfo* test_info) {
     return test_info->should_run() && test_info->result()->Passed();
   }
 
-  // Returns true if test skipped.
+  // Returns true if and only if test skipped.
   static bool TestSkipped(const TestInfo* test_info) {
     return test_info->should_run() && test_info->result()->Skipped();
   }
 
-  // Returns true if test failed.
+  // Returns true if and only if test failed.
   static bool TestFailed(const TestInfo* test_info) {
     return test_info->should_run() && test_info->result()->Failed();
   }
 
-  // Returns true if the test is disabled and will be reported in the XML
-  // report.
+  // Returns true if and only if the test is disabled and will be reported in
+  // the XML report.
   static bool TestReportableDisabled(const TestInfo* test_info) {
     return test_info->is_reportable() && test_info->is_disabled_;
   }
 
-  // Returns true if test is disabled.
+  // Returns true if and only if test is disabled.
   static bool TestDisabled(const TestInfo* test_info) {
     return test_info->is_disabled_;
   }
 
-  // Returns true if this test will appear in the XML report.
+  // Returns true if and only if this test will appear in the XML report.
   static bool TestReportable(const TestInfo* test_info) {
     return test_info->is_reportable();
   }
@@ -1014,7 +1014,7 @@
   internal::SetUpTestSuiteFunc set_up_tc_;
   // Pointer to the function that tears down the test suite.
   internal::TearDownTestSuiteFunc tear_down_tc_;
-  // True if any test in this test suite should run.
+  // True if and only if any test in this test suite should run.
   bool should_run_;
   // The start time, in milliseconds since UNIX Epoch.
   TimeInMillis start_timestamp_;
@@ -1349,11 +1349,12 @@
   // Gets the elapsed time, in milliseconds.
   TimeInMillis elapsed_time() const;
 
-  // Returns true if the unit test passed (i.e. all test suites passed).
+  // Returns true if and only if the unit test passed (i.e. all test suites
+  // passed).
   bool Passed() const;
 
-  // Returns true if the unit test failed (i.e. some test suite failed
-  // or something outside of all tests failed).
+  // Returns true if and only if the unit test failed (i.e. some test suite
+  // failed or something outside of all tests failed).
   bool Failed() const;
 
   // Gets the i-th test suite among all the test suites. i can range from 0 to
@@ -2265,10 +2266,9 @@
   ::testing::ScopedTrace GTEST_CONCAT_TOKEN_(gtest_trace_, __LINE__)(\
     __FILE__, __LINE__, (message))
 
-
 // Compile-time assertion for type equality.
-// StaticAssertTypeEq<type1, type2>() compiles if type1 and type2 are
-// the same type.  The value it returns is not interesting.
+// StaticAssertTypeEq<type1, type2>() compiles if and only if type1 and type2
+// are the same type.  The value it returns is not interesting.
 //
 // Instead of making StaticAssertTypeEq a class template, we make it a
 // function template that invokes a helper class template.  This
diff --git a/googletest/include/gtest/internal/gtest-filepath.h b/googletest/include/gtest/internal/gtest-filepath.h
index 5d21bbc..c11b101 100644
--- a/googletest/include/gtest/internal/gtest-filepath.h
+++ b/googletest/include/gtest/internal/gtest-filepath.h
@@ -110,7 +110,7 @@
                                          const FilePath& base_name,
                                          const char* extension);
 
-  // Returns true if the path is "".
+  // Returns true if and only if the path is "".
   bool IsEmpty() const { return pathname_.empty(); }
 
   // If input name has a trailing separator character, removes it and returns
diff --git a/googletest/include/gtest/internal/gtest-internal.h b/googletest/include/gtest/internal/gtest-internal.h
index 62af669..22127c7 100644
--- a/googletest/include/gtest/internal/gtest-internal.h
+++ b/googletest/include/gtest/internal/gtest-internal.h
@@ -189,7 +189,7 @@
 //   expected_value:      "5"
 //   actual_value:        "6"
 //
-// The ignoring_case parameter is true if the assertion is a
+// The ignoring_case parameter is true if and only if the assertion is a
 // *_STRCASEEQ*.  When it's true, the string " (ignoring case)" will
 // be inserted into the message.
 GTEST_API_ AssertionResult EqFailure(const char* expected_expression,
@@ -318,15 +318,15 @@
   // Returns the sign bit of this number.
   Bits sign_bit() const { return kSignBitMask & u_.bits_; }
 
-  // Returns true if this is NAN (not a number).
+  // Returns true if and only if this is NAN (not a number).
   bool is_nan() const {
     // It's a NAN if the exponent bits are all ones and the fraction
     // bits are not entirely zeros.
     return (exponent_bits() == kExponentBitMask) && (fraction_bits() != 0);
   }
 
-  // Returns true if this number is at most kMaxUlps ULP's away from
-  // rhs.  In particular, this function:
+  // Returns true if and only if this number is at most kMaxUlps ULP's away
+  // from rhs.  In particular, this function:
   //
   //   - returns false if either number is (or both are) NAN.
   //   - treats really large numbers as almost equal to infinity.
@@ -852,7 +852,7 @@
   typename std::remove_const<typename std::remove_reference<T>::type>::type
 
 // IsAProtocolMessage<T>::value is a compile-time bool constant that's
-// true if T is type proto2::Message or a subclass of it.
+// true if and only if T is type proto2::Message or a subclass of it.
 template <typename T>
 struct IsAProtocolMessage
     : public bool_constant<
diff --git a/googletest/include/gtest/internal/gtest-port.h b/googletest/include/gtest/internal/gtest-port.h
index 830aa19..0813adc 100644
--- a/googletest/include/gtest/internal/gtest-port.h
+++ b/googletest/include/gtest/internal/gtest-port.h
@@ -357,7 +357,8 @@
 #  include <android/api-level.h>  // NOLINT
 #endif
 
-// Defines this to true if Google Test can use POSIX regular expressions.
+// Defines this to true if and only if Google Test can use POSIX regular
+// expressions.
 #ifndef GTEST_HAS_POSIX_RE
 # if GTEST_OS_LINUX_ANDROID
 // On Android, <regex.h> is only available starting with Gingerbread.
@@ -398,7 +399,7 @@
 // The user didn't tell us whether exceptions are enabled, so we need
 // to figure it out.
 # if defined(_MSC_VER) && defined(_CPPUNWIND)
-// MSVC defines _CPPUNWIND to 1 if exceptions are enabled.
+// MSVC defines _CPPUNWIND to 1 if and only if exceptions are enabled.
 #  define GTEST_HAS_EXCEPTIONS 1
 # elif defined(__BORLANDC__)
 // C++Builder's implementation of the STL uses the _HAS_EXCEPTIONS
@@ -409,16 +410,17 @@
 #  endif  // _HAS_EXCEPTIONS
 #  define GTEST_HAS_EXCEPTIONS _HAS_EXCEPTIONS
 # elif defined(__clang__)
-// clang defines __EXCEPTIONS if exceptions are enabled before clang 220714,
-// but if cleanups are enabled after that. In Obj-C++ files, there can be
-// cleanups for ObjC exceptions which also need cleanups, even if C++ exceptions
-// are disabled. clang has __has_feature(cxx_exceptions) which checks for C++
-// exceptions starting at clang r206352, but which checked for cleanups prior to
-// that. To reliably check for C++ exception availability with clang, check for
+// clang defines __EXCEPTIONS if and only if exceptions are enabled before clang
+// 220714, but if and only if cleanups are enabled after that. In Obj-C++ files,
+// there can be cleanups for ObjC exceptions which also need cleanups, even if
+// C++ exceptions are disabled. clang has __has_feature(cxx_exceptions) which
+// checks for C++ exceptions starting at clang r206352, but which checked for
+// cleanups prior to that. To reliably check for C++ exception availability with
+// clang, check for
 // __EXCEPTIONS && __has_feature(cxx_exceptions).
 #  define GTEST_HAS_EXCEPTIONS (__EXCEPTIONS && __has_feature(cxx_exceptions))
 # elif defined(__GNUC__) && __EXCEPTIONS
-// gcc defines __EXCEPTIONS to 1 if exceptions are enabled.
+// gcc defines __EXCEPTIONS to 1 if and only if exceptions are enabled.
 #  define GTEST_HAS_EXCEPTIONS 1
 # elif defined(__SUNPRO_CC)
 // Sun Pro CC supports exceptions.  However, there is no compile-time way of
@@ -426,7 +428,7 @@
 // they are enabled unless the user tells us otherwise.
 #  define GTEST_HAS_EXCEPTIONS 1
 # elif defined(__IBMCPP__) && __EXCEPTIONS
-// xlC defines __EXCEPTIONS to 1 if exceptions are enabled.
+// xlC defines __EXCEPTIONS to 1 if and only if exceptions are enabled.
 #  define GTEST_HAS_EXCEPTIONS 1
 # elif defined(__HP_aCC)
 // Exception handling is in effect by default in HP aCC compiler. It has to
@@ -467,13 +469,14 @@
 
 # ifdef _MSC_VER
 
-#  ifdef _CPPRTTI  // MSVC defines this macro if RTTI is enabled.
+#ifdef _CPPRTTI  // MSVC defines this macro if and only if RTTI is enabled.
 #   define GTEST_HAS_RTTI 1
 #  else
 #   define GTEST_HAS_RTTI 0
 #  endif
 
-// Starting with version 4.3.2, gcc defines __GXX_RTTI if RTTI is enabled.
+// Starting with version 4.3.2, gcc defines __GXX_RTTI if and only if RTTI is
+// enabled.
 # elif defined(__GNUC__)
 
 #  ifdef __GXX_RTTI
@@ -894,9 +897,9 @@
   // Returns the string representation of the regex.
   const char* pattern() const { return pattern_; }
 
-  // FullMatch(str, re) returns true if regular expression re matches
-  // the entire str.
-  // PartialMatch(str, re) returns true if regular expression re
+  // FullMatch(str, re) returns true if and only if regular expression re
+  // matches the entire str.
+  // PartialMatch(str, re) returns true if and only if regular expression re
   // matches a substring of str (including str itself).
   static bool FullMatch(const ::std::string& str, const RE& re) {
     return FullMatch(str.c_str(), re);
@@ -1238,7 +1241,8 @@
   void Reset(Handle handle);
 
  private:
-  // Returns true if the handle is a valid handle object that can be closed.
+  // Returns true if and only if the handle is a valid handle object that can be
+  // closed.
   bool IsCloseable() const;
 
   Handle handle_;
@@ -1340,7 +1344,8 @@
   // When non-NULL, used to block execution until the controller thread
   // notifies.
   Notification* const thread_can_start_;
-  bool finished_;  // true if we know that the thread function has finished.
+  bool finished_;  // true if and only if we know that the thread function has
+                   // finished.
   pthread_t thread_;  // The native thread object.
 
   GTEST_DISALLOW_COPY_AND_ASSIGN_(ThreadWithParam);
diff --git a/googletest/include/gtest/internal/gtest-string.h b/googletest/include/gtest/internal/gtest-string.h
index 26d8407..82aaa63 100644
--- a/googletest/include/gtest/internal/gtest-string.h
+++ b/googletest/include/gtest/internal/gtest-string.h
@@ -94,7 +94,8 @@
   static const char* Utf16ToAnsi(LPCWSTR utf16_str);
 #endif
 
-  // Compares two C strings.  Returns true if they have the same content.
+  // Compares two C strings.  Returns true if and only if they have the same
+  // content.
   //
   // Unlike strcmp(), this function can handle NULL argument(s).  A
   // NULL C string is considered different to any non-NULL C string,
@@ -107,16 +108,16 @@
   // returned.
   static std::string ShowWideCString(const wchar_t* wide_c_str);
 
-  // Compares two wide C strings.  Returns true if they have the same
-  // content.
+  // Compares two wide C strings.  Returns true if and only if they have the
+  // same content.
   //
   // Unlike wcscmp(), this function can handle NULL argument(s).  A
   // NULL C string is considered different to any non-NULL C string,
   // including the empty string.
   static bool WideCStringEquals(const wchar_t* lhs, const wchar_t* rhs);
 
-  // Compares two C strings, ignoring case.  Returns true if they
-  // have the same content.
+  // Compares two C strings, ignoring case.  Returns true if and only if
+  // they have the same content.
   //
   // Unlike strcasecmp(), this function can handle NULL argument(s).
   // A NULL C string is considered different to any non-NULL C string,
@@ -124,8 +125,8 @@
   static bool CaseInsensitiveCStringEquals(const char* lhs,
                                            const char* rhs);
 
-  // Compares two wide C strings, ignoring case.  Returns true if they
-  // have the same content.
+  // Compares two wide C strings, ignoring case.  Returns true if and only if
+  // they have the same content.
   //
   // Unlike wcscasecmp(), this function can handle NULL argument(s).
   // A NULL C string is considered different to any non-NULL wide C string,
@@ -139,8 +140,8 @@
   static bool CaseInsensitiveWideCStringEquals(const wchar_t* lhs,
                                                const wchar_t* rhs);
 
-  // Returns true if the given string ends with the given suffix, ignoring
-  // case. Any string is considered to end with an empty suffix.
+  // Returns true if and only if the given string ends with the given suffix,
+  // ignoring case. Any string is considered to end with an empty suffix.
   static bool EndsWithCaseInsensitive(
       const std::string& str, const std::string& suffix);
 
diff --git a/googletest/samples/prime_tables.h b/googletest/samples/prime_tables.h
index 4178e70..72539bf 100644
--- a/googletest/samples/prime_tables.h
+++ b/googletest/samples/prime_tables.h
@@ -43,7 +43,7 @@
  public:
   virtual ~PrimeTable() {}
 
-  // Returns true if n is a prime number.
+  // Returns true if and only if n is a prime number.
   virtual bool IsPrime(int n) const = 0;
 
   // Returns the smallest prime number greater than p; or returns -1
diff --git a/googletest/samples/sample1.cc b/googletest/samples/sample1.cc
index 58dbf17..1d42759 100644
--- a/googletest/samples/sample1.cc
+++ b/googletest/samples/sample1.cc
@@ -41,7 +41,7 @@
   return result;
 }
 
-// Returns true if n is a prime number.
+// Returns true if and only if n is a prime number.
 bool IsPrime(int n) {
   // Trivial case 1: small numbers
   if (n <= 1) return false;
diff --git a/googletest/samples/sample1.h b/googletest/samples/sample1.h
index a90eae4..12e49de 100644
--- a/googletest/samples/sample1.h
+++ b/googletest/samples/sample1.h
@@ -35,7 +35,7 @@
 // Returns n! (the factorial of n).  For negative n, n! is defined to be 1.
 int Factorial(int n);
 
-// Returns true if n is a prime number.
+// Returns true if and only if n is a prime number.
 bool IsPrime(int n);
 
 #endif  // GTEST_SAMPLES_SAMPLE1_H_
diff --git a/googletest/src/gtest-death-test.cc b/googletest/src/gtest-death-test.cc
index e5ec287..da09a1c 100644
--- a/googletest/src/gtest-death-test.cc
+++ b/googletest/src/gtest-death-test.cc
@@ -122,8 +122,8 @@
     "Indicates the file, line number, temporal index of "
     "the single death test to run, and a file descriptor to "
     "which a success code may be sent, all separated by "
-    "the '|' characters.  This flag is specified if and only if the current "
-    "process is a sub-process launched for running a thread-safe "
+    "the '|' characters.  This flag is specified if and only if the "
+    "current process is a sub-process launched for running a thread-safe "
     "death test.  FOR INTERNAL USE ONLY.");
 }  // namespace internal
 
@@ -563,8 +563,8 @@
 //   status_ok: true if exit_status is acceptable in the context of
 //              this particular death test, which fails if it is false
 //
-// Returns true if all of the above conditions are met.  Otherwise, the
-// first failing condition, in the order given above, is the one that is
+// Returns true if and only if all of the above conditions are met.  Otherwise,
+// the first failing condition, in the order given above, is the one that is
 // reported. Also sets the last death test message string.
 bool DeathTestImpl::Passed(bool status_ok) {
   if (!spawned())
diff --git a/googletest/src/gtest-internal-inl.h b/googletest/src/gtest-internal-inl.h
index e29d992..8ed70da 100644
--- a/googletest/src/gtest-internal-inl.h
+++ b/googletest/src/gtest-internal-inl.h
@@ -99,14 +99,14 @@
 // A valid random seed must be in [1, kMaxRandomSeed].
 const int kMaxRandomSeed = 99999;
 
-// g_help_flag is true if the --help flag or an equivalent form is
-// specified on the command line.
+// g_help_flag is true if and only if the --help flag or an equivalent form
+// is specified on the command line.
 GTEST_API_ extern bool g_help_flag;
 
 // Returns the current time in milliseconds.
 GTEST_API_ TimeInMillis GetTimeInMillis();
 
-// Returns true if Google Test should use colors in the output.
+// Returns true if and only if Google Test should use colors in the output.
 GTEST_API_ bool ShouldUseColor(bool stdout_is_tty);
 
 // Formats the given time in milliseconds as seconds.
@@ -266,8 +266,8 @@
 GTEST_API_ Int32 Int32FromEnvOrDie(const char* env_var, Int32 default_val);
 
 // Given the total number of shards, the shard index, and the test id,
-// returns true if the test should be run on this shard. The test id is
-// some arbitrary but unique non-negative integer assigned to each test
+// returns true if and only if the test should be run on this shard. The test id
+// is some arbitrary but unique non-negative integer assigned to each test
 // method. Assumes that 0 <= shard_index < total_shards.
 GTEST_API_ bool ShouldRunTestOnShard(
     int total_shards, int shard_index, int test_id);
@@ -352,7 +352,7 @@
   // TestPropertyKeyIs has NO default constructor.
   explicit TestPropertyKeyIs(const std::string& key) : key_(key) {}
 
-  // Returns true if the test name of test property matches on key_.
+  // Returns true if and only if the test name of test property matches on key_.
   bool operator()(const TestProperty& test_property) const {
     return test_property.key() == key_;
   }
@@ -385,15 +385,15 @@
 
   // Functions for processing the gtest_filter flag.
 
-  // Returns true if the wildcard pattern matches the string.  The
-  // first ':' or '\0' character in pattern marks the end of it.
+  // Returns true if and only if the wildcard pattern matches the string.
+  // The first ':' or '\0' character in pattern marks the end of it.
   //
   // This recursive algorithm isn't very efficient, but is clear and
   // works well enough for matching test names, which are short.
   static bool PatternMatchesString(const char *pattern, const char *str);
 
-  // Returns true if the user-specified filter matches the test suite
-  // name and the test name.
+  // Returns true if and only if the user-specified filter matches the test
+  // suite name and the test name.
   static bool FilterMatchesTest(const std::string& test_suite_name,
                                 const std::string& test_name);
 
@@ -577,11 +577,12 @@
   // Gets the elapsed time, in milliseconds.
   TimeInMillis elapsed_time() const { return elapsed_time_; }
 
-  // Returns true if the unit test passed (i.e. all test suites passed).
+  // Returns true if and only if the unit test passed (i.e. all test suites
+  // passed).
   bool Passed() const { return !Failed(); }
 
-  // Returns true if the unit test failed (i.e. some test suite failed
-  // or something outside of all tests failed).
+  // Returns true if and only if the unit test failed (i.e. some test suite
+  // failed or something outside of all tests failed).
   bool Failed() const {
     return failed_test_suite_count() > 0 || ad_hoc_test_result()->Failed();
   }
@@ -911,7 +912,7 @@
   // desired.
   OsStackTraceGetterInterface* os_stack_trace_getter_;
 
-  // True if PostFlagParsingInit() has been called.
+  // True if and only if PostFlagParsingInit() has been called.
   bool post_flag_parse_init_performed_;
 
   // The random number seed used at the beginning of the test run.
diff --git a/googletest/src/gtest-port.cc b/googletest/src/gtest-port.cc
index 9024f03..73dfdeb 100644
--- a/googletest/src/gtest-port.cc
+++ b/googletest/src/gtest-port.cc
@@ -715,7 +715,7 @@
   free(const_cast<char*>(pattern_));
 }
 
-// Returns true if regular expression re matches the entire str.
+// Returns true if and only if regular expression re matches the entire str.
 bool RE::FullMatch(const char* str, const RE& re) {
   if (!re.is_valid_) return false;
 
@@ -723,8 +723,8 @@
   return regexec(&re.full_regex_, str, 1, &match, 0) == 0;
 }
 
-// Returns true if regular expression re matches a substring of str
-// (including str itself).
+// Returns true if and only if regular expression re matches a substring of
+// str (including str itself).
 bool RE::PartialMatch(const char* str, const RE& re) {
   if (!re.is_valid_) return false;
 
@@ -764,14 +764,14 @@
 
 #elif GTEST_USES_SIMPLE_RE
 
-// Returns true if ch appears anywhere in str (excluding the
+// Returns true if and only if ch appears anywhere in str (excluding the
 // terminating '\0' character).
 bool IsInSet(char ch, const char* str) {
   return ch != '\0' && strchr(str, ch) != nullptr;
 }
 
-// Returns true if ch belongs to the given classification.  Unlike
-// similar functions in <ctype.h>, these aren't affected by the
+// Returns true if and only if ch belongs to the given classification.
+// Unlike similar functions in <ctype.h>, these aren't affected by the
 // current locale.
 bool IsAsciiDigit(char ch) { return '0' <= ch && ch <= '9'; }
 bool IsAsciiPunct(char ch) {
@@ -784,13 +784,13 @@
       ('0' <= ch && ch <= '9') || ch == '_';
 }
 
-// Returns true if "\\c" is a supported escape sequence.
+// Returns true if and only if "\\c" is a supported escape sequence.
 bool IsValidEscape(char c) {
   return (IsAsciiPunct(c) || IsInSet(c, "dDfnrsStvwW"));
 }
 
-// Returns true if the given atom (specified by escaped and pattern)
-// matches ch.  The result is undefined if the atom is invalid.
+// Returns true if and only if the given atom (specified by escaped and
+// pattern) matches ch.  The result is undefined if the atom is invalid.
 bool AtomMatchesChar(bool escaped, char pattern_char, char ch) {
   if (escaped) {  // "\\p" where p is pattern_char.
     switch (pattern_char) {
@@ -828,7 +828,7 @@
 
   bool is_valid = true;
 
-  // True if ?, *, or + can follow the previous atom.
+  // True if and only if ?, *, or + can follow the previous atom.
   bool prev_repeatable = false;
   for (int i = 0; regex[i]; i++) {
     if (regex[i] == '\\') {  // An escape sequence
@@ -904,8 +904,8 @@
   return false;
 }
 
-// Returns true if regex matches a prefix of str.  regex must be a
-// valid simple regular expression and not start with "^", or the
+// Returns true if and only if regex matches a prefix of str. regex must
+// be a valid simple regular expression and not start with "^", or the
 // result is undefined.
 bool MatchRegexAtHead(const char* regex, const char* str) {
   if (*regex == '\0')  // An empty regex matches a prefix of anything.
@@ -935,8 +935,8 @@
   }
 }
 
-// Returns true if regex matches any substring of str.  regex must be
-// a valid simple regular expression, or the result is undefined.
+// Returns true if and only if regex matches any substring of str.  regex must
+// be a valid simple regular expression, or the result is undefined.
 //
 // The algorithm is recursive, but the recursion depth doesn't exceed
 // the regex length, so we won't need to worry about running out of
@@ -964,13 +964,13 @@
   free(const_cast<char*>(full_pattern_));
 }
 
-// Returns true if regular expression re matches the entire str.
+// Returns true if and only if regular expression re matches the entire str.
 bool RE::FullMatch(const char* str, const RE& re) {
   return re.is_valid_ && MatchRegexAnywhere(re.full_pattern_, str);
 }
 
-// Returns true if regular expression re matches a substring of str
-// (including str itself).
+// Returns true if and only if regular expression re matches a substring of
+// str (including str itself).
 bool RE::PartialMatch(const char* str, const RE& re) {
   return re.is_valid_ && MatchRegexAnywhere(re.pattern_, str);
 }
@@ -1330,7 +1330,7 @@
 // Reads and returns the Boolean environment variable corresponding to
 // the given flag; if it's not set, returns default_value.
 //
-// The value is considered true if it's not "0".
+// The value is considered true if and only if it's not "0".
 bool BoolFromGTestEnv(const char* flag, bool default_value) {
 #if defined(GTEST_GET_BOOL_FROM_ENV_)
   return GTEST_GET_BOOL_FROM_ENV_(flag, default_value);
diff --git a/googletest/src/gtest.cc b/googletest/src/gtest.cc
index 0d1f413..a5b4e5a 100644
--- a/googletest/src/gtest.cc
+++ b/googletest/src/gtest.cc
@@ -177,8 +177,8 @@
 // stack trace.
 const char kStackTraceMarker[] = "\nStack trace:\n";
 
-// g_help_flag is true if the --help flag or an equivalent form is
-// specified on the command line.
+// g_help_flag is true if and only if the --help flag or an equivalent form
+// is specified on the command line.
 bool g_help_flag = false;
 
 // Utilty function to Open File for Writing
@@ -215,15 +215,14 @@
     "Run disabled tests too, in addition to the tests normally being run.");
 
 GTEST_DEFINE_bool_(
-    break_on_failure,
-    internal::BoolFromGTestEnv("break_on_failure", false),
-    "True if a failed assertion should be a debugger break-point.");
+    break_on_failure, internal::BoolFromGTestEnv("break_on_failure", false),
+    "True if and only if a failed assertion should be a debugger "
+    "break-point.");
 
-GTEST_DEFINE_bool_(
-    catch_exceptions,
-    internal::BoolFromGTestEnv("catch_exceptions", true),
-    "True if " GTEST_NAME_
-    " should catch exceptions and treat them as test failures.");
+GTEST_DEFINE_bool_(catch_exceptions,
+                   internal::BoolFromGTestEnv("catch_exceptions", true),
+                   "True if and only if " GTEST_NAME_
+                   " should catch exceptions and treat them as test failures.");
 
 GTEST_DEFINE_string_(
     color,
@@ -270,17 +269,13 @@
     "executable's name and, if necessary, made unique by adding "
     "digits.");
 
-GTEST_DEFINE_bool_(
-    print_time,
-    internal::BoolFromGTestEnv("print_time", true),
-    "True if " GTEST_NAME_
-    " should display elapsed time in text output.");
+GTEST_DEFINE_bool_(print_time, internal::BoolFromGTestEnv("print_time", true),
+                   "True if and only if " GTEST_NAME_
+                   " should display elapsed time in text output.");
 
-GTEST_DEFINE_bool_(
-    print_utf8,
-    internal::BoolFromGTestEnv("print_utf8", true),
-    "True if " GTEST_NAME_
-    " prints UTF8 characters as text.");
+GTEST_DEFINE_bool_(print_utf8, internal::BoolFromGTestEnv("print_utf8", true),
+                   "True if and only if " GTEST_NAME_
+                   " prints UTF8 characters as text.");
 
 GTEST_DEFINE_int32_(
     random_seed,
@@ -294,16 +289,14 @@
     "How many times to repeat each test.  Specify a negative number "
     "for repeating forever.  Useful for shaking out flaky tests.");
 
-GTEST_DEFINE_bool_(
-    show_internal_stack_frames, false,
-    "True if " GTEST_NAME_ " should include internal stack frames when "
-    "printing test failure stack traces.");
+GTEST_DEFINE_bool_(show_internal_stack_frames, false,
+                   "True if and only if " GTEST_NAME_
+                   " should include internal stack frames when "
+                   "printing test failure stack traces.");
 
-GTEST_DEFINE_bool_(
-    shuffle,
-    internal::BoolFromGTestEnv("shuffle", false),
-    "True if " GTEST_NAME_
-    " should randomize tests' order on every run.");
+GTEST_DEFINE_bool_(shuffle, internal::BoolFromGTestEnv("shuffle", false),
+                   "True if and only if " GTEST_NAME_
+                   " should randomize tests' order on every run.");
 
 GTEST_DEFINE_int32_(
     stack_trace_depth,
@@ -354,7 +347,7 @@
   return state_ % range;
 }
 
-// GTestIsInitialized() returns true if the user has initialized
+// GTestIsInitialized() returns true if and only if the user has initialized
 // Google Test.  Useful for catching the user mistake of not initializing
 // Google Test before calling RUN_ALL_TESTS().
 static bool GTestIsInitialized() { return GetArgvs().size() > 0; }
@@ -371,18 +364,18 @@
   return sum;
 }
 
-// Returns true if the test suite passed.
+// Returns true if and only if the test suite passed.
 static bool TestSuitePassed(const TestSuite* test_suite) {
   return test_suite->should_run() && test_suite->Passed();
 }
 
-// Returns true if the test suite failed.
+// Returns true if and only if the test suite failed.
 static bool TestSuiteFailed(const TestSuite* test_suite) {
   return test_suite->should_run() && test_suite->Failed();
 }
 
-// Returns true if test_suite contains at least one test that should
-// run.
+// Returns true if and only if test_suite contains at least one test that
+// should run.
 static bool ShouldRunTestSuite(const TestSuite* test_suite) {
   return test_suite->should_run();
 }
@@ -482,8 +475,8 @@
   return result.string();
 }
 
-// Returns true if the wildcard pattern matches the string.  The
-// first ':' or '\0' character in pattern marks the end of it.
+// Returns true if and only if the wildcard pattern matches the string.
+// The first ':' or '\0' character in pattern marks the end of it.
 //
 // This recursive algorithm isn't very efficient, but is clear and
 // works well enough for matching test names, which are short.
@@ -525,8 +518,8 @@
   }
 }
 
-// Returns true if the user-specified filter matches the test suite
-// name and the test name.
+// Returns true if and only if the user-specified filter matches the test
+// suite name and the test name.
 bool UnitTestOptions::FilterMatchesTest(const std::string& test_suite_name,
                                         const std::string& test_name) {
   const std::string& full_name = test_suite_name + "." + test_name.c_str();
@@ -910,7 +903,8 @@
 
 #endif  // GTEST_OS_WINDOWS_MOBILE
 
-// Compares two C strings.  Returns true if they have the same content.
+// Compares two C strings.  Returns true if and only if they have the same
+// content.
 //
 // Unlike strcmp(), this function can handle NULL argument(s).  A NULL
 // C string is considered different to any non-NULL C string,
@@ -1320,7 +1314,7 @@
 //   lhs_value:      "5"
 //   rhs_value:      "6"
 //
-// The ignoring_case parameter is true if the assertion is a
+// The ignoring_case parameter is true if and only if the assertion is a
 // *_STRCASEEQ*.  When it's true, the string "Ignoring case" will
 // be inserted into the message.
 AssertionResult EqFailure(const char* lhs_expression,
@@ -1563,9 +1557,9 @@
 
 // Helper functions for implementing IsSubString() and IsNotSubstring().
 
-// This group of overloaded functions return true if needle is a
-// substring of haystack.  NULL is considered a substring of itself
-// only.
+// This group of overloaded functions return true if and only if needle
+// is a substring of haystack.  NULL is considered a substring of
+// itself only.
 
 bool IsSubstringPred(const char* needle, const char* haystack) {
   if (needle == nullptr || haystack == nullptr) return needle == haystack;
@@ -1865,8 +1859,8 @@
   return internal::WideStringToUtf8(wide_c_str, -1);
 }
 
-// Compares two wide C strings.  Returns true if they have the same
-// content.
+// Compares two wide C strings.  Returns true if and only if they have the
+// same content.
 //
 // Unlike wcscmp(), this function can handle NULL argument(s).  A NULL
 // C string is considered different to any non-NULL C string,
@@ -1910,7 +1904,7 @@
                             << " vs " << PrintToString(s2);
 }
 
-// Compares two C strings, ignoring case.  Returns true if they have
+// Compares two C strings, ignoring case.  Returns true if and only if they have
 // the same content.
 //
 // Unlike strcasecmp(), this function can handle NULL argument(s).  A
@@ -1922,18 +1916,18 @@
   return posix::StrCaseCmp(lhs, rhs) == 0;
 }
 
-  // Compares two wide C strings, ignoring case.  Returns true if they
-  // have the same content.
-  //
-  // Unlike wcscasecmp(), this function can handle NULL argument(s).
-  // A NULL C string is considered different to any non-NULL wide C string,
-  // including the empty string.
-  // NB: The implementations on different platforms slightly differ.
-  // On windows, this method uses _wcsicmp which compares according to LC_CTYPE
-  // environment variable. On GNU platform this method uses wcscasecmp
-  // which compares according to LC_CTYPE category of the current locale.
-  // On MacOS X, it uses towlower, which also uses LC_CTYPE category of the
-  // current locale.
+// Compares two wide C strings, ignoring case.  Returns true if and only if they
+// have the same content.
+//
+// Unlike wcscasecmp(), this function can handle NULL argument(s).
+// A NULL C string is considered different to any non-NULL wide C string,
+// including the empty string.
+// NB: The implementations on different platforms slightly differ.
+// On windows, this method uses _wcsicmp which compares according to LC_CTYPE
+// environment variable. On GNU platform this method uses wcscasecmp
+// which compares according to LC_CTYPE category of the current locale.
+// On MacOS X, it uses towlower, which also uses LC_CTYPE category of the
+// current locale.
 bool String::CaseInsensitiveWideCStringEquals(const wchar_t* lhs,
                                               const wchar_t* rhs) {
   if (lhs == nullptr) return rhs == nullptr;
@@ -1956,7 +1950,7 @@
 #endif  // OS selector
 }
 
-// Returns true if str ends with the given suffix, ignoring case.
+// Returns true if and only if str ends with the given suffix, ignoring case.
 // Any string is considered to end with an empty suffix.
 bool String::EndsWithCaseInsensitive(
     const std::string& str, const std::string& suffix) {
@@ -2198,12 +2192,12 @@
   return result.skipped();
 }
 
-// Returns true if the test was skipped.
+// Returns true if and only if the test was skipped.
 bool TestResult::Skipped() const {
   return !Failed() && CountIf(test_part_results_, TestPartSkipped) > 0;
 }
 
-// Returns true if the test failed.
+// Returns true if and only if the test failed.
 bool TestResult::Failed() const {
   for (int i = 0; i < total_part_count(); ++i) {
     if (GetTestPartResult(i).failed())
@@ -2212,22 +2206,22 @@
   return false;
 }
 
-// Returns true if the test part fatally failed.
+// Returns true if and only if the test part fatally failed.
 static bool TestPartFatallyFailed(const TestPartResult& result) {
   return result.fatally_failed();
 }
 
-// Returns true if the test fatally failed.
+// Returns true if and only if the test fatally failed.
 bool TestResult::HasFatalFailure() const {
   return CountIf(test_part_results_, TestPartFatallyFailed) > 0;
 }
 
-// Returns true if the test part non-fatally failed.
+// Returns true if and only if the test part non-fatally failed.
 static bool TestPartNonfatallyFailed(const TestPartResult& result) {
   return result.nonfatally_failed();
 }
 
-// Returns true if the test has a non-fatal failure.
+// Returns true if and only if the test has a non-fatal failure.
 bool TestResult::HasNonfatalFailure() const {
   return CountIf(test_part_results_, TestPartNonfatallyFailed) > 0;
 }
@@ -2523,18 +2517,18 @@
       this, &Test::TearDown, "TearDown()");
 }
 
-// Returns true if the current test has a fatal failure.
+// Returns true if and only if the current test has a fatal failure.
 bool Test::HasFatalFailure() {
   return internal::GetUnitTestImpl()->current_test_result()->HasFatalFailure();
 }
 
-// Returns true if the current test has a non-fatal failure.
+// Returns true if and only if the current test has a non-fatal failure.
 bool Test::HasNonfatalFailure() {
   return internal::GetUnitTestImpl()->current_test_result()->
       HasNonfatalFailure();
 }
 
-// Returns true if the current test was skipped.
+// Returns true if and only if the current test was skipped.
 bool Test::IsSkipped() {
   return internal::GetUnitTestImpl()->current_test_result()->Skipped();
 }
@@ -2633,7 +2627,7 @@
   explicit TestNameIs(const char* name)
       : name_(name) {}
 
-  // Returns true if the test name of test_info matches name_.
+  // Returns true if and only if the test name of test_info matches name_.
   bool operator()(const TestInfo * test_info) const {
     return test_info && test_info->name() == name_;
   }
@@ -2992,7 +2986,7 @@
 
 #endif  // GTEST_OS_WINDOWS && !GTEST_OS_WINDOWS_MOBILE
 
-// Returns true if Google Test should use colors in the output.
+// Returns true if and only if Google Test should use colors in the output.
 bool ShouldUseColor(bool stdout_is_tty) {
   const char* const gtest_color = GTEST_FLAG(color).c_str();
 
@@ -4709,11 +4703,12 @@
   return impl()->elapsed_time();
 }
 
-// Returns true if the unit test passed (i.e. all test suites passed).
+// Returns true if and only if the unit test passed (i.e. all test suites
+// passed).
 bool UnitTest::Passed() const { return impl()->Passed(); }
 
-// Returns true if the unit test failed (i.e. some test suite failed
-// or something outside of all tests failed).
+// Returns true if and only if the unit test failed (i.e. some test suite
+// failed or something outside of all tests failed).
 bool UnitTest::Failed() const { return impl()->Failed(); }
 
 // Gets the i-th test suite among all the test suites. i can range from 0 to
@@ -5161,7 +5156,7 @@
   // Constructor.
   explicit TestSuiteNameIs(const std::string& name) : name_(name) {}
 
-  // Returns true if the name of test_suite matches name_.
+  // Returns true if and only if the name of test_suite matches name_.
   bool operator()(const TestSuite* test_suite) const {
     return test_suite != nullptr &&
            strcmp(test_suite->name(), name_.c_str()) == 0;
@@ -5232,7 +5227,8 @@
 // All other functions called from RunAllTests() may safely assume that
 // parameterized tests are ready to be counted and run.
 bool UnitTestImpl::RunAllTests() {
-  // True if Google Test is initialized before RUN_ALL_TESTS() is called.
+  // True if and only if Google Test is initialized before RUN_ALL_TESTS() is
+  // called.
   const bool gtest_is_initialized_before_run_all_tests = GTestIsInitialized();
 
   // Do not run any test if the --help flag was specified.
@@ -5248,7 +5244,7 @@
   // protocol.
   internal::WriteToShardStatusFileIfNeeded();
 
-  // True if we are in a subprocess for running a thread-safe-style
+  // True if and only if we are in a subprocess for running a thread-safe-style
   // death test.
   bool in_subprocess_for_death_test = false;
 
@@ -5281,7 +5277,7 @@
   random_seed_ = GTEST_FLAG(shuffle) ?
       GetRandomSeedFromFlag(GTEST_FLAG(random_seed)) : 0;
 
-  // True if at least one test has failed.
+  // True if and only if at least one test has failed.
   bool failed = false;
 
   TestEventListener* repeater = listeners()->repeater();
@@ -5479,8 +5475,8 @@
 }
 
 // Given the total number of shards, the shard index, and the test id,
-// returns true if the test should be run on this shard. The test id is
-// some arbitrary but unique non-negative integer assigned to each test
+// returns true if and only if the test should be run on this shard. The test id
+// is some arbitrary but unique non-negative integer assigned to each test
 // method. Assumes that 0 <= shard_index < total_shards.
 bool ShouldRunTestOnShard(int total_shards, int shard_index, int test_id) {
   return (test_id % total_shards) == shard_index;
@@ -6053,7 +6049,7 @@
 void ParseGoogleTestFlagsOnly(int* argc, char** argv) {
   ParseGoogleTestFlagsOnlyImpl(argc, argv);
 
-  // Fix the value of *_NSGetArgc() on macOS, but if
+  // Fix the value of *_NSGetArgc() on macOS, but if and only if
   // *_NSGetArgv() == argv
   // Only applicable to char** version of argv
 #if GTEST_OS_MAC
diff --git a/googletest/test/googletest-death-test-test.cc b/googletest/test/googletest-death-test-test.cc
index 814d771..cba906c 100644
--- a/googletest/test/googletest-death-test-test.cc
+++ b/googletest/test/googletest-death-test-test.cc
@@ -141,7 +141,7 @@
       DieInside("MemberFunction");
   }
 
-  // True if MemberFunction() should die.
+  // True if and only if MemberFunction() should die.
   bool should_die_;
   const FilePath original_dir_;
 };
@@ -158,7 +158,7 @@
   }
 
  private:
-  // True if MemberFunction() should die.
+  // True if and only if MemberFunction() should die.
   bool should_die_;
 };
 
@@ -573,8 +573,8 @@
   }, "died but not with expected error");
 }
 
-// On exit, *aborted will be true if the EXPECT_DEATH() statement
-// aborted the function.
+// On exit, *aborted will be true if and only if the EXPECT_DEATH()
+// statement aborted the function.
 void ExpectDeathTestHelper(bool* aborted) {
   *aborted = true;
   EXPECT_DEATH(DieIf(false), "DieIf");  // This assertion should fail.
diff --git a/googletest/test/googletest-throw-on-failure-test.py b/googletest/test/googletest-throw-on-failure-test.py
index a38cd33..ea627c4 100755
--- a/googletest/test/googletest-throw-on-failure-test.py
+++ b/googletest/test/googletest-throw-on-failure-test.py
@@ -86,7 +86,7 @@
                         variable; None if the variable should be unset.
       flag_value:       value of the --gtest_break_on_failure flag;
                         None if the flag should not be present.
-      should_fail:      True if the program is expected to fail.
+      should_fail:      True if and only if the program is expected to fail.
     """
 
     SetEnvVar(THROW_ON_FAILURE, env_var_value)
diff --git a/googletest/test/gtest_environment_test.cc b/googletest/test/gtest_environment_test.cc
index 58908e6..064bfc5 100644
--- a/googletest/test/gtest_environment_test.cc
+++ b/googletest/test/gtest_environment_test.cc
@@ -116,7 +116,7 @@
   }
 }
 
-// Runs the tests.  Return true if successful.
+// Runs the tests.  Return true if and only if successful.
 //
 // The 'failure' parameter specifies the type of failure that should
 // be generated by the global set-up.
diff --git a/googletest/test/gtest_pred_impl_unittest.cc b/googletest/test/gtest_pred_impl_unittest.cc
index 4d77896..1afe5e2 100644
--- a/googletest/test/gtest_pred_impl_unittest.cc
+++ b/googletest/test/gtest_pred_impl_unittest.cc
@@ -144,10 +144,10 @@
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
@@ -539,10 +539,10 @@
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
@@ -976,10 +976,10 @@
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
@@ -1455,10 +1455,10 @@
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
@@ -1976,10 +1976,10 @@
     }
   }
 
-  // true if the test function is expected to run to finish.
+  // true if and only if the test function is expected to run to finish.
   static bool expected_to_finish_;
 
-  // true if the test function did run to finish.
+  // true if and only if the test function did run to finish.
   static bool finished_;
 
   static int n1_;
diff --git a/googletest/test/gtest_premature_exit_test.cc b/googletest/test/gtest_premature_exit_test.cc
index 777a8bf..1d1187e 100644
--- a/googletest/test/gtest_premature_exit_test.cc
+++ b/googletest/test/gtest_premature_exit_test.cc
@@ -45,7 +45,7 @@
 
 class PrematureExitTest : public Test {
  public:
-  // Returns true if the given file exists.
+  // Returns true if and only if the given file exists.
   static bool FileExists(const char* filepath) {
     StatStruct stat;
     return Stat(filepath, &stat) == 0;
@@ -61,7 +61,7 @@
     }
   }
 
-  // Returns true if the premature-exit file exists.
+  // Returns true if and only if the premature-exit file exists.
   bool PrematureExitFileExists() const {
     return FileExists(premature_exit_file_path_);
   }
diff --git a/googletest/test/gtest_test_utils.py b/googletest/test/gtest_test_utils.py
index abd56ec..ef9363c 100755
--- a/googletest/test/gtest_test_utils.py
+++ b/googletest/test/gtest_test_utils.py
@@ -215,10 +215,11 @@
     Returns:
       An object that represents outcome of the executed process. It has the
       following attributes:
-        terminated_by_signal   True if the child process has been terminated
-                               by a signal.
+        terminated_by_signal   True if and only if the child process has been
+                               terminated by a signal.
         signal                 Sygnal that terminated the child process.
-        exited                 True if the child process exited normally.
+        exited                 True if and only if the child process exited
+                               normally.
         exit_code              The code with which the child process exited.
         output                 Child process's stdout and stderr output
                                combined in a string.
diff --git a/googletest/test/gtest_unittest.cc b/googletest/test/gtest_unittest.cc
index 2c0552d..39749b7 100644
--- a/googletest/test/gtest_unittest.cc
+++ b/googletest/test/gtest_unittest.cc
@@ -2167,12 +2167,12 @@
 
 // First, some predicates and predicate-formatters needed by the tests.
 
-// Returns true if the argument is an even number.
+// Returns true if and only if the argument is an even number.
 bool IsEven(int n) {
   return (n % 2) == 0;
 }
 
-// A functor that returns true if the argument is an even number.
+// A functor that returns true if and only if the argument is an even number.
 struct IsEvenFunctor {
   bool operator()(int n) { return IsEven(n); }
 };
@@ -2216,13 +2216,13 @@
   }
 };
 
-// Returns true if the sum of the arguments is an even number.
+// Returns true if and only if the sum of the arguments is an even number.
 bool SumIsEven2(int n1, int n2) {
   return IsEven(n1 + n2);
 }
 
-// A functor that returns true if the sum of the arguments is an even
-// number.
+// A functor that returns true if and only if the sum of the arguments is an
+// even number.
 struct SumIsEven3Functor {
   bool operator()(int n1, int n2, int n3) {
     return IsEven(n1 + n2 + n3);