Consider the following example:

    auto concept A<class T> {
         int f(T);
    }

    auto concept B<class T> {

         int f(T)

         template<class U>
             requires A<U> // brings f(U') into scope
         auto g(T p, U q) ->
             decltype(f(p) + f(q));
             // Both B<T>::f(T) and A<U>::f(U) needed here
             // but B<T>::f(T) is hidden by A<U>::f(U)
             // (declared in the same scope as g's template parameters)
    }

This is similar to the case that motivated 11.4 [class.mem] paragraph 19:

A constrained member is treated as a constrained template (_N2914_.14.11 [temp.constrained]) whose template requirements include the requirements specified in its member-requirement clause and the requirements of each enclosing constrained template.

See also _N2914_.14.10.1.1 [concept.fct] paragraph 10 for a similar rule for default implementations.

A more general version of this merging of requirements is needed, but it does not appear to exist. _N2914_.14.11.1.2 [temp.req.impl] would seem to be the logical place for such a rule.