#include <stdio.h>  
#include <algorithm>  
#include <assert.h>
#include <bitset>
#include <cmath>  
#include <complex>  
#include <deque>  
#include <functional>  
#include <iostream>  
#include <limits.h>  
#include <map>  
#include <math.h>  
#include <queue>  
#include <deque>
#include <set>  
#include <stdlib.h>  
#include <string.h>  
#include <string>  
#include <time.h>  
#include <unordered_map>  
#include <unordered_set>  
#include <vector>  
#include <chrono>
#include <random>
#include <time.h>
#include <fstream>
#define ll long long
#define rep2(i,a,b) for(ll i=a;i<=b;++i)
#define rep(i,n) for(ll i=0;i<n;i++)
#define rep3(i,a,b) for(ll i=a;i>=b;i--)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pq priority_queue<int>
#define pqg priority_queue<int,vector<int>,greater<int>>
#define pb push_back
#define vec vector<int>
#define vecll vector<ll>
#define vecpii vector<pii>
#define endl "\n"
#define all(c) begin(c),end(c)
using namespace std;
int in() {int x;scanf("%d",&x);return x;}
ll lin() {ll x;scanf("%lld",&x);return x;}
void print(vec v){for(auto e:v)cout<<e<<" ";cout<<endl;}
void print(vecll v){for(auto e:v)cout<<e<<" ";cout<<endl;}
void print(map<int,int> mp){for(auto e:mp)cout<<e.first<<" "<<e.second<<endl;cout<<endl;}


#define INF 1e9+7
#define LLINF 1e18+7
#define N 250000

const ll MOD=1e9+7;
template <std::uint_fast64_t Modulus> class modint {
  using u64 = std::uint_fast64_t;

public:
  u64 a;

  constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {}
  constexpr u64 &value() noexcept { return a; }
  constexpr const u64 &value() const noexcept { return a; }
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    a += rhs.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (a < rhs.a) {
      a += Modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    a = a * rhs.a % Modulus;
    return *this;
  }
  constexpr modint &operator/=(modint rhs) noexcept {
    u64 exp = Modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }
};
ll int inv[N],comb[N],prd[N],invprd[N];
void calc_inv(){
    inv[1]=1;
    rep2(i,2,N-1){
        inv[i]=((-(MOD/i)*inv[MOD%i])%MOD+MOD)%MOD;
    }
    return;
}
void calc_comb(ll int n){
    comb[0]=1;
    rep2(i,1,n){
        comb[i]=comb[i-1]*(n+1-i)*inv[i]%MOD;
    }
    return;
}
void calc_product(){
    prd[0]=prd[1]=1;
    invprd[0]=invprd[1]=1;
    rep2(i,2,N-1){
        prd[i]=i*prd[i-1]%MOD;
        invprd[i]=inv[i]*invprd[i-1]%MOD;
    }
    return ;
}
void calc(){calc_inv();calc_product();}
modint<MOD> cmb(int a,int b){
    if(a<b)return 0;
    if(a<0||b<0)return 0;
    ll res=prd[a]*invprd[b]%MOD*invprd[a-b]%MOD;
    modint<MOD> RES=res;
    return RES;
}
ll modpow(ll x,ll n){
    if(n==0) return 1;
    ll res=modpow(x*x%MOD,n/2);
    if(n&1) res=res*x%MOD;
    return res;
}


#define mint modint<MOD>
main(){
    calc();
    mint ans=0;
    int h=in()-1,w=in()-1,a=in(),b=in();
    int d=h-a,r=w-b;
    rep(i,d+1){
        ans+=cmb(b+i-1,i)*cmb(r+h-i,r);
        // cout<<cmb(b+i-1,i).a<<" "<<cmb(r+h-i,r).a<<endl;
    }
    cout<<ans.a;
}

Measured memory_bytes: 8064