#include <bits/stdc++.h>

const int Mod=1e9+7,N=2e5+10;

int w,h,a,b,inv[N],fact[N];

void Init() {
	scanf("%d%d%d%d",&w,&h,&a,&b);
}

int Calc(int n,int m) { return 1ll*fact[n]*inv[n-m]%Mod*inv[m]%Mod; }

void Solve() {
	int n=w+h-2;
	fact[0]=1; for (int i=1;i<=n;++i) fact[i]=1ll*fact[i-1]*i%Mod;
	inv[0]=1; inv[1]=1;  for (int i=2;i<=n;++i) inv[i]=1ll*(Mod-Mod/i)*inv[Mod%i]%Mod;
	for (int i=2;i<=n;++i) inv[i]=1ll*inv[i]*inv[i-1]%Mod;
	int x=w-a,y=b+1,ans=0;
	while (x>=1 && y<=h) {
		ans=(ans+1ll*Calc(x+y-2,y-1)*Calc(w+h-x-y,w-x))%Mod;
		x--; y++;
	}
	printf("%d\n",ans);
}

int main() {
	Init();
	Solve();
	return 0;
}