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#include <vector>
#include <cstdio>
#include <stack>
#include <algorithm>
#include <queue>
#include <map>
#include <cmath>
#include <unordered_set>
#include <unordered_map>
#include <set>
#include <cstring>
#include <bitset>
#include <iostream>
#include <queue>
#include <iomanip>
#include <complex>

using namespace std;

#define ALL(x) x.begin(), x.end()
#define UNIQUE(c) (c).resize(unique(ALL(c)) - (c).begin())
#define FOR(i, a, b) for(int i =(a); i <=(b); ++i)
#define RE(i, n) FOR(i, 1, n)
#define RED(i, n) FORD(i, n, 1)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define REP(i, n) for(int i = 0;i <(n); ++i)
#define REPD(i, n) FORD(i, n-1,0)

const int maxn = 500012, mod = 1000000007, bis = 4096;
int d[maxn * 8], il[maxn], base, f[maxn], inf[maxn];
vector<int>v[maxn];
bitset<bis>bi[maxn];

void ins(int x, int y, int ak) {
    x += base; y += base;
    d[x] = ak; d[y] = ak;
    while (x/2 != y/2){
        if(!(x&1))d[x + 1] = ak;
        if(y&1)d[y - 1] = ak;
        x>>=1; y>>=1;
    }
}

int que(int x) {
    int odp = 0;
    x += base;
    while (x) {
        odp = max(odp, d[x]);
        x>>=1;
    }
    return odp;
}

int mul(int a, int b) {
    return int(a * 1ll * b % mod);
}

int binPow(int a, int k) {
    int ans = 1;
    while (k > 0) {
        if (k & 1)
            ans = mul(ans, a);
        a = mul(a, a);
        k >>= 1;
    }
    return ans;
}

void precalc(int n) {
    f[0] = inf[0] = 1;
    RE(i, n)f[i] = mul(f[i - 1], i);
    inf[n] = binPow(f[n], mod - 2);
    RED(i, n - 1)inf[i] = mul(inf[i + 1], i + 1);
}

int C(int n, int k) {
    if (k < 0 || n < k)
        return 0;
    return mul(f[n], mul(inf[n - k], inf[k]));
}

int norm(int a) {
    while (a >= mod)
        a -= mod;
    while (a < 0)
        a += mod;
    return a;
}

void solve() {
    int l, r, n;
    cin>>n;
    base = (1<<((int)log2(2 * n) + 1)) - 1;
    RE(i, n) {
        cin>>l>>r;
        auto le = que(l), re = que(r);
        if(le)v[i].push_back(le);
        if(re && le != re)v[i].push_back(re);
        ins(l, r, i);
    }
//    RE(i, n){
//        cout<<i<<" ";
//        for(auto ne: v[i])cout<<ne<<" ";
//        cout<<"\n";
//    }
    precalc(n + 1);
    for(int i = n; i >= 1; i -= bis){
        RE(j, i)bi[j].reset();
        REP(j, min(bis, i))bi[i - j][j] = true;
        RED(j, i) for(auto ne: v[j])bi[ne] |= bi[j];
        RE(j, i)il[j] += bi[j].count();
    }
    RE(i, n)il[i] --;
    int res = 0;
    RE(i, n) {
        auto pom =  mul(mul(f[il[i]], f[n - il[i] - 1]), C(n, n - il[i] - 1));
        res = norm(res + pom);
    }
    cout<<mul(res, inf[n])<<"\n";
}

int main() {
    ios_base::sync_with_stdio(false), cin.tie(nullptr);
    int tt = 1;
//    cin >> tt;
    while (tt--) {
        solve();
    }
    return 0;
}