https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77595
--- Comment #1 from Andrzej Krzemienski <akrzemi1 at gmail dot com> --- I mean, the expectation is that member functions whose constraints are not satisfied should be omitted during explicit class template instantiation. See this discussion for more background: https://groups.google.com/a/isocpp.org/forum/?fromgroups#!topic/concepts/EZZjh_kFiJY
