//CORRECT

template <int N>
struct ev{
};

static ev<0> ev_0;

template<int N>
static ev<N + 2> ev_SS(ev<N>);



//VS WRONG
template <int N>
struct ev{
	static ev<0> ev_0;

	template<int M>
	static ev<M + 2> ev_SS(ev<M>); //fails coz Coq enforces ev<N> return type here
};