#include <bits/stdc++.h>
using namespace std;
void io() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout.precision(15);
}
long long mulmod(long long a, long long b, long long m) {
  long long q = (long long)(((long double)a * (long double)b) / (long double)m);
  long long r = a * b - q * m;
  if (r > m) r %= m;
  if (r < 0) r += m;
  return r;
}
template <typename T>
T mod(T a, T b) {
  while (a < 0) a += b;
  return a % b;
}
template <typename T>
T power(T e, T n, T m) {
  T x = 1, p = e;
  while (n) {
    if (n & 1) x = mod(x * p, m);
    p = mod(p * p, m);
    n >>= 1;
  }
  return x;
}
template <typename T>
T power(T e, T n) {
  T x = 1, p = e;
  while (n) {
    if (n & 1) x = x * p;
    p = p * p;
    n >>= 1;
  }
  return x;
}
template <typename T>
T InverseEuler(T a, T m) {
  return (a == 1 ? 1 : power(a, m - 2, m));
}
template <typename T>
inline T gcd(T a, T b) {
  T c;
  while (b) {
    c = b;
    b = a % b;
    a = c;
  }
  return a;
}
template <typename T>
T lcm(T a, T b) {
  return (a * (b / gcd(a, b)));
}
long long exEuclid(long long a, long long b, long long &x, long long &y) {
  if (a == 0) {
    x = 0;
    y = 1;
    return b;
  }
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  long long x1, y1;
  long long g = exEuclid(b % a, a, x1, y1);
  x = y1 - (b / a) * x1;
  y = x1;
  return g;
}
const long long MOD = 1e9 + 7;
const int MAXN = 2e5 + 5;
long long fact[MAXN];
long long inv[MAXN];
long long C(int n, int r) {
  if (n < 0 || r > n) {
    return 0;
  }
  long long num = fact[n];
  long long den = (inv[r] * inv[n - r]) % MOD;
  return (num * den) % MOD;
}
long long get_ways(int i1, int j1, int i2, int j2) {
  if (i2 >= i1 && j2 >= j1) {
    return C(i2 - i1 + j2 - j1, i2 - i1);
  }
  return 0;
}
const int LN = 20;
const int MAXK = 2e3 + 5;
long long dp[LN][MAXK];
long long val[LN];
bool cmp(pair<int, int> a, pair<int, int> b) {
  return ((a.first + a.second) < (b.first + b.second));
}
pair<int, int> pts[MAXN];
int n, m;
int pcnt = 0;
int chk1 = 0, chk2 = 0;
int main(int argc, char *argv[]) {
  io();
  cin >> n >> m;
  fact[0] = 1;
  for (int i = 1; i < MAXN; i++) {
    fact[i] = 1ll * i * fact[i - 1];
    fact[i] %= MOD;
  }
  inv[MAXN - 1] = power(fact[MAXN - 1], MOD - 2, MOD);
  for (int i = MAXN - 2; i >= 0; i--) {
    inv[i] = 1ll * (i + 1) * inv[i + 1];
    inv[i] %= MOD;
  }
  int k, s;
  cin >> k >> s;
  int ln = 0;
  int x, y;
  for (int i = 0; i < k; i++) {
    cin >> x >> y;
    pts[++pcnt] = {x, y};
  }
  pts[++pcnt] = {n, m};
  sort(pts + 1, pts + pcnt + 1);
  long long fnum = 0;
  long long total = get_ways(1, 1, n, m);
  long long fdeno = power(total, MOD - 2, MOD);
  k = pcnt;
  for (int i = 1; i <= pcnt; i++) {
    dp[0][i] = get_ways(1, 1, pts[i].first, pts[i].second);
  }
  for (int i = 1; i <= pcnt; i++) {
    for (int j = 1; j < i; j++) {
      dp[0][i] = (dp[0][i] - (get_ways(pts[j].first, pts[j].second,
                                       pts[i].first, pts[i].second) *
                              dp[0][j]) %
                                 MOD);
      dp[0][i] += MOD;
      dp[0][i] %= MOD;
    }
  }
  for (int i = 1; i < LN; i++) {
    for (int j = 1; j <= pcnt; j++) {
      dp[i][j] = get_ways(1, 1, pts[j].first, pts[j].second);
      for (int p = 1; p < j; p++) {
        dp[i][j] = (dp[i][j] - (get_ways(pts[p].first, pts[p].second,
                                         pts[j].first, pts[j].second) *
                                dp[i][p]) %
                                   MOD);
        dp[i][j] = (dp[i][j] + MOD) % MOD;
      }
      for (int p = 0; p < i; p++) {
        dp[i][j] = (dp[i][j] - dp[p][j] + MOD) % MOD;
      }
    }
  }
  long long sub = total;
  for (int i = 0; i < LN; i++) {
    fnum = (fnum + dp[i][pcnt] * 1ll * s) % MOD;
    sub = (sub - dp[i][pcnt] + MOD) % MOD;
    s = (s + 1) / 2;
  }
  fnum = (fnum + sub + MOD) % MOD;
  long long fans = fnum * fdeno;
  fans %= MOD;
  cout << fans << '\n';
  return 0;
}
