#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <vector>
#include <queue>
#include <cmath>
using namespace std;
typedef long long ll;
const int N=100010;
const ll mod=1000000007;
ll f[N],h,w,a,b;
ll powmod(ll x,ll n)
{
    ll s=1;
    while(n)
    {
        if(n&1)
            s=(s*x)%mod;
        x=(x*x)%mod;
        n>>=1;
    }
    return s;
}
ll lucas(ll n,ll m)
{
    ll a=f[n],b=(f[m]*f[n-m])%mod;
    return (a*powmod(b,mod-2))%mod;
}
int main()
{
    f[0]=1;
    for(ll i=1;i<N;i++)
        f[i]=(f[i-1]*i)%mod;
    	scanf("%lld%lld%lld%lld",&h,&w,&a,&b);
        ll res=0;
        for(ll i=b+1;i<=w;i++)
        {
            ll tmp=(lucas(i-1+h-a-1,h-a-1)*lucas(w-i+a-1,w-i))%mod;
            res=(res+tmp)%mod;
        }
        printf("%lld\n",res);    
    return 0;
}