uva 11175

#include <bits/stdc++.h>
using namespace std;
const int maxn = 3E2 + 5;
int G1[maxn][maxn], G2[maxn][maxn], gx[maxn], gy[maxn], to[maxn], n, m, x, y, T, kase;
bool check()
{
	for (int i = n - 1; i >= 0; i--)
	{
		memset(to, 0, sizeof(to));
		for (int j = gy[i] - 1; j >= 0; j--)
			for (int k = gx[G2[i][j]] - 1; k >= 0; k--)
				to[G1[G2[i][j]][k]]++;
		for (int j = 0; j < n; j++)
			if (to[j] && to[j] != gy[i])
				return false;
	}
	return true;
}
int main(int argc, char const *argv[])
{
	ios::sync_with_stdio(false); cin.tie(NULL);
	cin >> T;
	while (T--)
	{
		cin >> n >> m;
		memset(G1, 0, sizeof(G1));
		memset(G2, 0, sizeof(G2));
		memset(gx, 0, sizeof(gx));
		memset(gy, 0, sizeof(gy));
		while (m--)
		{
			cin >> x >> y;
			G1[x][gx[x]++] = y;
			G2[y][gy[y]++] = x;
		}
		cout << "Case #" << ++kase << ": " << (check() ? "YES" : "NO") << endl;
	}
	return 0;
}