Proposed resolution:

This wording is relative to N4081 in regard to fundamental-ts changes.

1. Edit §3.2.2 [tuple.apply] paragraph 2:

   template <class F, class Tuple>
   constexpr decltype(auto) apply(F&& f, Tuple&& t);
   

   -2- Effects: Given the exposition only function

   template <class F, class Tuple, size_t... I>
   constexpr decltype(auto) apply_impl(  // exposition only
       F&& f, Tuple&& t, index_sequence<I...>) {
     return INVOKE(std::forward<F>(f)(, std::get<I>(std::forward<Tuple>(t))...);
   }
   

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