[Bug libstdc++/71771] DR 685 applied incorrectly

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71771

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This fails without the single-type overloads:

#include <iterator>

namespace greedy {
    struct X { };

    template<typename T> X operator-(T, T) { return {}; }
}

int main()
{
    std::move_iterator<greedy::X*> m{nullptr};
    m - m;
    std::reverse_iterator<greedy::X*> r{nullptr};
    r - r;
}

Whether we still care about such unconstrained templates is another matter.