#include<iostream>
#include<cstring>
#include<cstdio>
#define maxn 200009
#define mo 1000000007
using namespace std;
typedef long long ll;
ll ans,f[maxn],last;
int n,m,a,b;
ll pow(ll x,int t)
{
  ll now=x,sum=1;
  while (t)
  {
  	if (t&1) sum=(sum*now)%mo;
  	now=(now*now)%mo;
  	t=t>>1;
  }
  return sum;
}
ll calc(int x,int y)
{
  ll di=pow((f[x-y]*f[y])%mo,mo-2);
  return ((di*f[x])%mo);
}
int main()
{
  scanf("%d%d%d%d",&n,&m,&a,&b);
  a=n-a+1;
  f[0]=1;
  for (int i=1;i<=n+m;i++) f[i]=(f[i-1]*i)%mo;
  int  x=a-1,rx=n-x;
  for (int i=b+1;i<=m;i++)
  {
  	int ry=m-i+1;
  	ans=(ans+(calc(x+i-2,x-1)*calc(rx+ry-2,ry-1))%mo)%mo;
  }
  //cout<<calc(n+m-2,n-1)<<endl;
  printf("%lld\n",ans);
  return 0;
}