Description：

Solution：

Code：

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstdio>

#include<cmath>

#include<cctype>

#include<cstring>

using namespace std;

int n;

#define MAXN 19

struct edges{int u,v;}es[MAXN][MAXN * MAXN / 2];

int m[MAXN];

int cnt(int k)

{

	int res = 1;

	while(k > 0)res += (k & 1),k = k >> 1;

	res = ((n - res) & 1) ? -1 : 1;

	return res;

}

typedef long long ll;

ll g[MAXN][MAXN];

#define MOD 1000000007

ll power(ll a,int b)

{

	ll res = 1;

	while(b > 0)

	{

		if(b & 1)res = res * a % MOD;

		a = a * a % MOD;

		b = b >> 1;

	}

	return res;

}

ll matrixtree(int k)

{

	memset(g,0,sizeof(g));

	for(int i = 1;i < n;++i)

	{

		if(k & (1 << (i - 1)))

		{

			for(int l = 1;l <= m[i];++l)

			{

				int u = es[i][l].u,v = es[i][l].v;

				++g[u][u];++g[v][v];

				--g[u][v];--g[v][u];

			}

		}

	}

	ll ans = 1;

	for(int i = 1;i < n;++i)

	{

		for(int j = i;j < n;++j)

		{

			if(g[j][i] != 0)

			{

				if(j != i)

				{

					for(int l = 1;l < n;++l)swap(g[i][l],g[j][l]);

					ans *= -1;

				}

				break;

			}

		}

		for(int j = i + 1;j < n;++j)

		{

			ll ratio = g[j][i] * power(g[i][i],MOD - 2) % MOD;

			for(int l = 1;l < n;++l)

			{

				g[j][l] = (g[j][l] - g[i][l] * ratio % MOD + MOD) % MOD;

			}

		}

	}

	ans = (ans + MOD) % MOD;

	for(int i = 1;i < n;++i)ans = ans * g[i][i] % MOD;

	return ans;

}

int main()

{

	scanf("%d",&n);

	for(int i = 1;i < n;++i)

	{

		scanf("%d",&m[i]);

		for(int k = 1;k <= m[i];++k)

		{

			scanf("%d%d",&es[i][k].u,&es[i][k].v);

		}

	}

	int ans = 0;

	for(int i = 1;i < (1 << (n - 1));++i)

	{

		ans = (ans + cnt(i) * matrixtree(i) % MOD + MOD) % MOD;

	}

	cout << ans << endl;

	return 0;

}