#include <iostream>
#include <cstdio>

using namespace std;

typedef long long ll;

const int M = 1000000007;

ll h, w, a, b, ans;
ll fac[200005];

ll pow(ll p, ll q) {
    ll re = 1;
    for(; q; q >>= 1, p = p * p % M) {
        if(q&1) re = re * p % M;
    }
    return re;
}

int main()
{
    scanf("%lld%lld%lld%lld", &h, &w, &a, &b);
    fac[0] = 1;
    for(ll i = 1; i <= 200000; i++) fac[i] = fac[i - 1] * i % M;
    for(ll i = b; i < w; i++)
    {
        ll h1 = h - a - 1;
        ll t1 = fac[h1 + i] * pow(fac[h1], M - 2) % M * pow(fac[i], M - 2) % M;
        ll h2 = a - 1;
        ll t2 = fac[h2 + w - i - 1] * pow(fac[h2], M - 2) % M * pow(fac[w - i - 1], M - 2) % M;
        ans += t1 * t2;
        ans %= M;
    }
    printf("%lld", ans);
    return 0;
}
