#include<cstdio>
using namespace std;
int h,w,a,b,ans;
const int mm=1000000007;
int fff(int m,int n){
	if(m==0) return 1;
	else{
		int i,j=2*mm,k=n-m;
	    float sth=1;
	    for(i=1;i<=k;i++)
	    {
		    sth=sth*(i+m)/i;
		    while(sth>j) sth-=mm;
	    }
	    j=sth;
	    return j;
	}
}
int main(){
	scanf("%d%d%d%d",&h,&w,&a,&b);
	int x,y,tha=h-a,twb=w-b;
	for(x=1;x<=tha;x++)
	{
		ans+=fff(x-1,x+b-1)*fff(h-x,h-x+twb-1)%mm;
		ans=ans%mm;
	}
	printf("%d",ans);
	return 0;
}