Rationale:

Fixed by N2292 Standard Library Applications for Deleted Functions.

Proposed resolution:

Remove the above mentioned two function templates from the header <functional> synopsis ([function.objects])

template<class Function1, class Function2>
void operator==(const function<Function1>&, const function<Function2>&);
template<class Function1, class Function2>
void operator!=(const function<Function1>&, const function<Function2>&);

The header <functional> synopsis in [function.objects] contains the following two free comparison operator templates for the function class template

template<class Function1, class Function2>
void operator==(const function<Function1>&, const function<Function2>&);
template<class Function1, class Function2>
void operator!=(const function<Function1>&, const function<Function2>&);

which are nowhere described. I assume that they are relicts before the corresponding two private and undefined member templates in the function template (see [func.wrap.func] and [func.wrap.func.undef]) have been introduced. The original free function templates should be removed, because using an undefined entity would lead to an ODR violation of the user.