func_code_string: #include <bits/stdc++.h>   using namespace std;   long long mod = 1e9 + 7;   long long po(long long x, long long y, long long p) {     long long res = 1;     x = x % p;     if (x == 0) return 0;     while (y > 0) {       if (y & 1) res = (res * x) % p;       y = y >> 1;       x = (x * x) % p;     }     return res;   }   void dfs(vector<vector<long long> > &adj, long long s, long long e,            vector<long long> &v, vector<bool> &vis) {     if (s == e) return;     vis[s] = true;     for (auto vx : adj[s]) {       if (!vis[vx]) {         dfs(adj, vx, e, v, vis);       }     }     v.push_back(s);   }   void solve() {     long long n, m, a, b;     cin >> n >> m >> a >> b;     vector<vector<long long> > adj(n + 1);     while (m--) {       long long x, y;       cin >> x >> y;       adj[x].push_back(y);       adj[y].push_back(x);     }     vector<long long> v1;     vector<long long> v2;     vector<bool> vis(n + 1, false);     dfs(adj, a, b, v1, vis);     for (int i = 0; i < n + 1; i++) vis[i] = false;     dfs(adj, b, a, v2, vis);     sort((v1).begin(), (v1).end());     sort((v2).begin(), (v2).end());     long long n1 = 0, n2 = 0;     for (long long i = 0; i < v1.size(); i++) {       if (!binary_search(v2.begin(), v2.end(), v1[i]) and v1[i] != a) {         n1++;       }     }     for (long long i = 0; i < v2.size(); i++) {       if (!binary_search(v1.begin(), v1.end(), v2[i]) and v2[i] != b) n2++;     }     cout << n1 * n2 <<   n ;   }   int main() {     ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);     int t = 1;     cin >> t;     while (t--) {       solve();     }     return 0;   }   