#include <limits.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <algorithm>
#include <cassert>
#include <cfloat>
#include <complex>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <vector>

using namespace std;

#define chmax(x, y) x = max(x, y)
#define chmin(x, y) x = min(x, y)
#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define repLRE(i, l, r) for (ll i = (l); i <= (r); ++i)
#define rrepLRE(i, l, r) for (ll i = (l); i >= (r); --i)
#define Sort(v) sort(v.begin(), v.end())
#define rSort(v) sort(v.rbegin(), v.rend())
#define Reverse(v) reverse(v.begin(), v.end())
#define Lower_bound(v, x) \
  distance(v.begin(), lower_bound(v.begin(), v.end(), x))
#define Upper_bound(v, x) \
  distance(v.begin(), upper_bound(v.begin(), v.end(), x))

using ll = long long;
using ull = unsigned long long;
using P = pair<ll, ll>;
using T = tuple<ll, ll, ll>;
using vll = vector<ll>;
using vP = vector<P>;
using vT = vector<T>;
using vvll = vector<vector<ll>>;
using vvP = vector<vector<P>>;
using dqll = deque<ll>;

ll dx[9] = {-1, 1, 0, 0, -1, -1, 1, 1, 0};
ll dy[9] = {0, 0, -1, 1, -1, 1, -1, 1, 0};

/* Macros reg. ends here */

const ll INF = 1LL << 50;
static const long long mod = 1000000007;
struct mint {
  ll x;  // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod - a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1) a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint& operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream& operator>>(istream& is, mint& a) { return is >> a.x; }
ostream& operator<<(ostream& os, const mint& a) { return os << a.x; }

class modutils {
  vector<mint> fact, invfact;

 public:
  modutils(int n = 200005) : fact(n + 1), invfact(n + 1) {
    fact[0] = 1;
    for (int i = 1; i <= n; i++) fact[i] = fact[i - 1] * i;
    invfact[n] = fact[n].inv();
    for (int i = n; i >= 1; i--) invfact[i - 1] = invfact[i] * i;
  }
  mint pow(mint x, ll n) { return x.pow(n); }
  mint comb(ll n, ll k) {
    if (n < 0 || k < 0 || n < k) return 0;
    return fact[n] * invfact[k] * invfact[n - k];
  }
  mint perm(ll n, ll k) {
    if (n < 0 || k < 0 || n < k) return 0;
    return fact[n] * invfact[n - k];
  }
  mint fac(ll n) { return fact[n]; }
};

int main() {
  cout << fixed << setprecision(15);

  ll h, w, a, b;
  cin >> h >> w >> a >> b;

  modutils mu;
  mint ans = 0;
  repLRE(j, b, w - 1){
    ll nn = j + h - a - 1;
    mint add = mu.comb(nn, j);
    ll mm = h - 1 + w - 1 - nn - 1;
    add *= mu.comb(mm, a - 1);
    ans += add;
  }

  cout << ans << endl;

  return 0;
}



Measured memory_bytes: 6428