Although the proposal explicitly does not include a reversed() function, it does mention one:
For example, this propsal could have included a
reversed()function on the difference type that would return a new difference that would undo the application of the original.
I would highly recommend against such a function. We already have a reversed() on over ninety varieties of collections and sequences, and they all return a new collection with the same elements, but in reverse order as the original.
If this function is to ever be implemented, it should be called inversed() or something like that.