template <Sequence S, typename T>
    requires Equality_comparable<Value_type<S>, T>
Iterator_of<S> find(S& seq, const T& value);

//that is equivalent to
template <class S, typename T>
    requires Sequence<S> && Equality_comparable<Value_type<S>, T>            
Iterator_of<S> find(S& seq, const T& value);