> > N3923 A SFINAE-Friendly iterator_traits
> __cpp_lib_experimental_iterator_traits_sfinae 201402 <iterator>
> > N3843 A SFINAE-Friendly common_type
> __cpp_lib_experimental_common_type_sfinae 201402 <type_traits>
>
> Weren't these removed from the TS and accepted as DRs against
> C++14?

Apparently so, as LWG issue 2409.

I must admit, at first I misunderstood "against C++14" as implying "to
C++14", and had a little adrenaline reaction that I missed it. But the fix
is actually applied to C++17. [whew]

On the other hand, this means we need to start keeping track of new features
in C++17. Fortunately, these proposals were both from Walter, whose
diligence compels him to include feature-test macro names in his proposals,
so that work is already done for us.

Clark