/*
        _            _                  _            _       _     _         _   _          _          _             _        
       / /\         / /\               / /\         / /\    / /\  /\ \      /\_\/\_\ _     /\ \       /\ \     _    /\ \      
      / /  \       / /  \             / /  \       / / /   / / /  \ \ \    / / / / //\_\   \ \ \     /  \ \   /\_\ /  \ \     
     / / /\ \__   / / /\ \           / / /\ \__   / /_/   / / /   /\ \_\  /\ \/ \ \/ / /   /\ \_\   / /\ \ \_/ / // /\ \_\    
    / / /\ \___\ / / /\ \ \         / / /\ \___\ / /\ \__/ / /   / /\/_/ /  \____\__/ /   / /\/_/  / / /\ \___/ // / /\/_/    
    \ \ \ \/___// / /  \ \ \        \ \ \ \/___// /\ \___\/ /   / / /   / /\/________/   / / /    / / /  \/____// / / ______  
     \ \ \     / / /___/ /\ \        \ \ \     / / /\/___/ /   / / /   / / /\/_// / /   / / /    / / /    / / // / / /\_____\ 
 _    \ \ \   / / /_____/ /\ \   _    \ \ \   / / /   / / /   / / /   / / /    / / /   / / /    / / /    / / // / /  \/____ / 
/_/\__/ / /  / /_________/\ \ \ /_/\__/ / /  / / /   / / /___/ / /__ / / /    / / /___/ / /__  / / /    / / // / /_____/ / /  
\ \/___/ /  / / /_       __\ \_\\ \/___/ /  / / /   / / //\__\/_/___\\/_/    / / //\__\/_/___\/ / /    / / // / /______\/ /   
 \_____\/   \_\___\     /____/_/ \_____\/   \/_/    \/_/ \/_________/        \/_/ \/_________/\/_/     \/_/ \/___________/    
                                                                                                                              
*/
#include<bits/stdc++.h>
using namespace std;
#define ALL(obj) (obj).begin(), (obj).end()
#define rsort(obj) sort(ALL(obj)); reverse(ALL(obj))
#define REP(i, n) for(int i = 0;i < (n);++i)

#define endl '\n'
#define pb emplace_back
#define mkp make_pair
#define p_q priority_queue
#define INF 1000000000
#define LLINF 1145141919810LL
#define PI 3.1415926
#define coutdb cout << fixed << setprecision(10)

const int dx[]={1,0,-1,0}, dy[]={0,-1,0,1};
const int dx_8[]={1,1,0,-1,-1,-1,0,1}, dy_8[]={0,-1,-1,-1,0,1,1,1};
const long long MOD = 1e9+7;

// typedef long long ll;
#define int long long

template <typename T> inline T GCD(T a,T b){T c;while(b!=0){c=a%b;a=b;b=c;}return a;}
template <typename T> inline T LCM(T a,T b){T c=GCD(a,b);a/=c;return a*b;}
template <typename T> inline T nCr(T a,T b){T i,r=1;for(i=1;i<=b;i++){r*=(a+1-i);r/=i;}return r;}
template <typename T> inline T nHr(T a,T b){return nCr(a+b-1,b);}

int fact[201000], revfact[201000];
queue<int> prime_count;

int powmod(int a, int p){
    int res = 1, tmp = a;
    while(p != 0){
        if(p % 2) res = (res*tmp) % MOD;
        tmp = (tmp*tmp) % MOD;
        p /= 2;
    }
    return res;
}

void factmod(){
    fact[0] = revfact[0] = 1;
    for(int i = 1; i < 201000; i++){
        fact[i] = (fact[i-1] * i) % MOD;
        revfact[i] = (revfact[i-1] * powmod(i, MOD-2)) % MOD;
    }
}

int nCrmod(int n, int r){ // nCr % MOD
    return (((fact[n] * revfact[r]) % MOD) * revfact[n-r]) % MOD;
}

signed main(void){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int H, W, A, B; cin >> H >> W >> A >> B;
  factmod();
  int ans = 0;
  for(int i = 1; i <= H-A; i++){
    int num = nCrmod(i-1+B-1, B-1);
    num *= nCrmod(H-i+W-B-1, H-i);
    num %= MOD;
    ans += num; ans %= MOD;
  }
  cout << ans << endl;
}

Measured memory_bytes: 3456