#include<bits/stdc++.h>
using namespace std;
const int mod=1e9+7;
long long fac[200005],inv[200005],fx[200005];
int h,w,a,b;
int work(int n,int m)
{
	return 1ll*fac[n]%mod*fx[m]%mod*fx[n-m]%mod;
}
int main()
{
	fac[0]=1;fac[1]=1;for(int i=2;i<=200000;++i)fac[i]=1ll*fac[i-1]*i%mod;
	inv[0]=1;inv[1]=1;for(int i=2;i<=200000;++i)inv[i]=1ll*(mod-mod/i)*inv[mod%i]%mod;
	fx[0]=1;fx[1]=1;for(int i=2;i<=200000;++i)fx[i]=1ll*inv[i]%mod*fx[i-1]%mod;
	while(~scanf("%d%d%d%d",&h,&w,&a,&b)){
	a=h-a;b++;
	long long ans=0;
	for(int i=1;i<=a;++i)
	{
		ans=(ans+1ll*work(b-2+i-1,b-2)%mod*work(h-i+w-b,h-i))%mod;
	}
	printf("%lld\n",ans);
	}
	return 0;
}