#include "bits/stdc++.h"
#define YES "YES"
#define NO "NO"
#define YESNO OUT(three(solve(),YES,NO))
#define ECHO OUT(solve())
#define three(A,B,C) ((A)?(B):(C))
#define FOR(i,a,b)  for(LL i=(a);i< (LL)(b);i++)
#define EFOR(i,a,b) for(LL i=(a);i<=(LL)(b);i++)
#define RFOR(i,a,b) for(LL i=(b);i>=(LL)(a);i--)
#define REP(i,b) FOR(i,zero,b)
#define EREP(i,b) EFOR(i,zero,b)
#define RREP(i,b) RFOR(i,b,zero)
#define ALL(c) c.begin(),c.end()
#define UNIQUE(c) sort(ALL(c));c.erase(unique(ALL(c)),c.end())
#define MAX(c) (*max_element(ALL(c)))
#define MIN(c) (*min_element(ALL(c)))
#define MP make_pair
#define FI first
#define SE second
#define SI(x) (LL(x.size()))
#define PB push_back
#define DEBUG(a) OUT(a)
#define DEBUG2(a,b) OUT2(a,b)
#define cat cout << __LINE__ << endl
#define OUT(a) cout << (a) << endl
#define OUT2(a,b) cout << (a) <<" "<<(b) << endl
#define zero 0LL
#define int long long
#define pb emplace_back
#define eb pb
using namespace std;
template<typename T> inline void maximize(T &a, T b) { a = max(a, b); }
template<typename T> inline void minimize(T &a, T b) { a = min(a, b); }
template<typename T> inline bool middle(T a, T b, T c) { return b <= a && a <= c; }
template<class T> inline bool MX(T &l, const T &r) { return l < r ? l = r, 1 : 0; }
template<class T> inline bool MN(T &l, const T &r) { return l > r ? l = r, 1 : 0; }
typedef int LL;
typedef double ld;
typedef int ut;
typedef vector<ut> VI;
typedef vector<VI> VII;
typedef pair<ut, ut> pr;
typedef pair<ut, pr> ppr;
typedef vector<pr> Vpr;
typedef vector<ppr> Vppr;
typedef tuple<int, int, int, int> tapu;
typedef vector<tapu> Vtapu;
typedef priority_queue<tapu, Vtapu, greater<tapu> > PQ;
inline void outputVI(VI x) { REP(i, SI(x)) { cout << three(i, " ", "") << x[i]; }OUT(""); }
const int SIZE1 = 2e5 + 1000;
const int SIZE2 = 2010;
const int SIZE3 = 430;
const int SIZE = SIZE1;
const int MAPSIZE = 40;
const LL p = 7 + 1e9;
const LL INF = 1LL << 60;
const long double EPS = 1e-7;
typedef pair<ld, ut> pld;
#define endl "\n" //インタラクティブでは消す
//ut A,B,C,D,E,F,G,H,I,J,O,P,Q,R,T,U;
ut N, M, K, L, Q, D, H, W;
VI edges[SIZE];
LL vals[SIZE], maps2[SIZE2][SIZE2], answer = zero;
LL maps[SIZE2][SIZE2];
int A[SIZE],B[SIZE];
LL times[SIZE2][SIZE2];
LL fact[SIZE], gyaku[SIZE];
inline LL nCr(LL n, LL r) {
	return fact[n] * gyaku[n - r]%p * gyaku[r]%p;
}
inline LL twin(LL a1, LL b1, LL a2, LL b2) {
	return nCr(a1 + b1 + a2 + b2, a1 + a2);
}
LL modpow(LL n, LL r) {
	if (r == 0) return 1;
	LL ans = modpow(n*n%p, r / 2);
	if (r % 2) ans *= n;
	return ans % p;
}
LL rev(LL x) {
	return modpow(x, p - 2);
}
LL solve() {
	cin >> N;
	fact[0] = 1;
	gyaku[0] = 1;
	EFOR(i, 1, SIZE2 * 4) fact[i] = fact[i - 1] * i%p;
	EFOR(i, 1, SIZE2*4) gyaku[i] = gyaku[i - 1] * rev(i)%p;
//	cout << nCr(8000, 4000) << endl;
	REP(i, N) {
		cin >> A[i] >> B[i];
		times[A[i]][B[i]]++;
	}
	LL ans = 0;
	RFOR(i,0,SIZE2*2) {
	//	cout << i << endl;
		REP(a, i) {
			LL b = i - a;
			if (max(a, b) >= SIZE2) continue;
			if (a <= 0 or b <= 0) continue;
			times[a-1][b] += times[a][b];
			times[a][b - 1] += times[a][b];
			times[a - 1][b] %= p;
			times[a][b - 1] %= p;
			ans -= twin(a, b - 1, a - 1, b)*times[a][b]%p;
			ans += p;
			times[a][b] = 0;
			ans %= p;
		}
	}
	LL ansc = 0;
	REP(i, SIZE2) REP(j, SIZE2) {
		if (i == j) continue;
		LL resa = twin(i, 0, j, 0);
		LL resb = twin(i, 0, 0, j);
		ansc += resa*times[i][0]%p*times[j][0]%p;
		ansc += resb*times[i][0]%p*times[0][j]%p;
		ansc += resb*times[0][i]%p*times[j][0]%p;
		ansc += resa*times[0][i]%p*times[0][j]%p;
		ansc %= p;
	}
	ans += gyaku[2] % p*ansc;
//	cout << "OK" << endl;
	REP(i, SIZE2){
		ans += twin(i, 0, i, 0) % p*(times[i][0]*(times[i][0]-1)/2) % p;
		ans += twin(0, i, 0, i) % p*(times[0][i]*(times[0][i]-1)/2) % p;
		ans += twin(i, 0, 0, i) % p*times[i][0] % p*(times[0][i]) % p;
		ans %= p;
	}
	cout << ans << endl;
	return 0;
}




//!!!!!!!!!!!!!!!!!!!実装を詰める!!!!!!!!!!!!!!!!!!!!!!!!!
signed main() {

	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(0);
	solve();
	cin >> N;
	return 0;

}


Measured memory_bytes: 42112