#include <cstdio>
#include <algorithm>
#include <vector>
#define file(x) freopen(#x".in", "r", stdin), freopen(#x".out", "w", stdout)

inline int read()
{
	int data = 0, w = 1; char ch = getchar();
	while (ch != '-' && (ch < '0' || ch > '9')) ch = getchar();
	if (ch == '-') w = -1, ch = getchar();
	while (ch >= '0' && ch <= '9') data = data * 10 + (ch ^ 48), ch = getchar();
	return data * w;
}

const int N(2e5 + 10), Mod(1e9 + 7);
int fac[N], inv[N], f[N], n, m, A, B;
int C(int n, int m) { return 1ll * fac[n + m] * inv[m] % Mod * inv[n] % Mod; }
int fastpow(int x, int y)
{
	int ans = 1;
	for (; y; y >>= 1, x = 1ll * x * x % Mod)
		if (y & 1) ans = 1ll * ans * x % Mod;
	return ans;
}

int main()
{
	n = read() - 1, m = read() - 1, A = read() - 1, B = read() - 1, fac[0] = inv[0] = 1;
	if (A == n || B == m) return puts("0"), 0;
	for (int i = 1; i <= n + m; i++) fac[i] = 1ll * fac[i - 1] * i % Mod;
	inv[n + m] = fastpow(fac[n + m], Mod - 2);
	for (int i = n + m - 1; i; i--) inv[i] = 1ll * inv[i + 1] * (i + 1) % Mod;
	int ans = C(n, m);
	for (int i = 0; i <= A; i++)
		ans = (ans - 1ll * C(i, m - B - 1) * C(n - i, B) % Mod + Mod) % Mod;
	printf("%d\n", ans);
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
#define int long long
const int mod=1e9+7;
 
int h,w,a,b,fac[200006],ans=0,inv_fac[200006];
int binpow(int x,int y){
	if(y==0) return 1;
	else{
		long long tmp=binpow(x,y/2);
		if(y%2==1) return ((tmp*tmp)%mod*x)%mod;
		else return (tmp*tmp)%mod;
	}
}
 
int C(int k,int n) {
	return fac[n]*inv_fac[k]%mod*inv_fac[n-k]%mod;
}
 
int path(int x1,int y1,int x2,int y2) {
	if(x1>x2||y1>y2) return 1;
	return  C(x2-x1,x2-x1+y2-y1)%mod;
}
 
signed main() {
	cin>>h>>w>>a>>b;
	fac[0]=1;
	inv_fac[0]=1;
	for(int i=1;i<=200005;++i) 
	{
		fac[i]=((i % mod)*fac[i-1])%mod;
		inv_fac[i]=binpow(fac[i],mod-2)%mod;
	}
	for(int i=1;i<=h-a;++i) {
		ans+=((path(1,1,i,b)%mod)*(path(i,b+1,h,w)%mod))%mod;
	}
	cout<<ans%mod;
}