In the example in _N2914_.14.10.1.1 [concept.fct] paragraph 10,

    concept EqualityComparable<typename T> {
      bool operator==(T, T);
      bool operator!=(T x, T y) { return !(x == y); }
    }

is the call to operator== in the default implementation well-formed, or is another requirement needed to allow the arguments to be passed by value? If another requirement is needed, should it be added in this example, or should the rules for implicit requirements be changed so that the example is well-formed?