#include<iostream>
#include<string.h>
#include<vector>
#include<algorithm>
using namespace std;
#define ll long long 
#define ull unsigned long long
#define pb push_back
const int maxn = 200005;
const ll mod = 1000000007;
ll f[maxn], n, m, A, B;
ll powmod(ll x, ll n)
{
	ll s = 1;
	while (n)
	{
		if (n & 1)
			s = (s * x) % mod;
		x = (x * x) % mod;
		n >>= 1;
	}
	return s;
}
ll C(ll n, ll m)
{
	ll a = f[n];
	ll b = (f[m] * f[n - m]) % mod;
	return (a * powmod(b, mod - 2)) % mod;
}
int main()
{
	f[0] = 1;
	for (ll i = 1; i < maxn; i++)
		f[i] = (f[i - 1] * i) % mod;
	cin >> n >> m >> A >> B;
		ll ans = 0;
		for (ll i = B + 1; i <= m; i++)
		{
			ll t = (C(i - 1 + n - A - 1, n - A - 1) * C(m - i + A - 1, m - i)) % mod;
			ans = (ans + t) % mod;
		}
		cout << ans << endl;
	return 0;
}