Proposed resolution:

This wording is relative to N4861.

1. Modify [iterator.traits] as indicated:

   -2- The definitions in this subclause make use of the following exposition-only concepts:

   template<class I>
   concept cpp17-iterator =
     copyable<I> && requires(I i) {
       { *i } -> can-reference;
       { ++i } -> same_as<I&>;
       { *i++ } -> can-reference;
     } && copyable<I>;
     
   […]