func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long mod = 1e9 + 7;   long long modpow(long long a, long long x) {     long long tmp = x;     long long val = a;     long long ret = 1LL;     while (tmp > 0) {       if (tmp % 2 == 1) ret = ret * val % mod;       val = val * val % mod;       tmp /= 2;     }     return ret;   }   long long modinv(long long a) { return modpow(a, mod - 2); }   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     int n;     cin >> n;     vector<long long> a(n);     for (int i = 0; i < n; i++) cin >> a[i];     vector<vector<long long>> G(1 << n, vector<long long>(n, 1));     for (int i = 0; i < (1 << n); i++) {       for (int j = 0; j < n; j++) {         if (((i >> j) & 1) == 0) continue;         for (int k = 0; k < n; k++) {           G[i][k] = G[i][k] * a[j] % mod * modinv(a[j] + a[k]) % mod;         }       }     }     long long ans = 0LL;     vector<long long> P(1 << n);     for (int i = 1; i < (1 << n); i++) {       long long cnt = __builtin_popcount(i);       long long P_tmp = 1LL;       for (int j = i; j > 0; j = ((j - 1) & i)) {         if (j == i) continue;         long long G_tmp0 = 1LL;         for (int k = 0; k < n; k++) {           if (((j >> k) & 1) == 1) continue;           if (((i >> k) & 1) == 0) continue;           G_tmp0 = (G_tmp0 * G[j][k]) % mod;         }         P_tmp = (P_tmp - P[j] * G_tmp0 % mod + mod) % mod;       }       long long G_tmp1 = 1LL;       for (int k = 0; k < n; k++) {         if (((i >> k) & 1) == 1) continue;         G_tmp1 = (G_tmp1 * G[i][k]) % mod;       }       ans = (ans + cnt * P_tmp % mod * G_tmp1) % mod;       P[i] = P_tmp;     }     cout << ans <<   n ;     return 0;   }   