error[E0252]: the name `core` is defined multiple times
  --> $DIR/rename.rs:2:5
   |
LL | use core;
   |     ---- previous import of the module `core` here
LL | use std as core;
   |     ^^^^^^^^^^^ `core` reimported here
   |
   = note: `core` must be defined only once in the type namespace of this module
help: you can use `as` to change the binding name of the import
   |
LL | use std as other_core;
   |     ^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0252`.