#include <iostream>
#include <fstream>
#include <string> 
#include <cmath>  
#include <cstdlib>
#include <ctime>
#include <vector>
#include <algorithm>
#include <numeric>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>
#include <functional>

using namespace std;
using ll = long long;
using ull = unsigned long long;

#define FOR(i, m, n) for(int i = int(m);i < int(n);i++)
#define REFOR(i, m, n) for(int i = int(n - 1);i >= int(m);i--)
#define REP(i,n) for(int i = 0; i < int(n); i++)
#define REREP(i,n) for(int i = int(n - 1); i >= 0; i--)
#define VI vector<int>
#define VVI vector<vector<int>>
#define VVVI vector<vector<vector<int>>>
#define VL vector<ll>
#define VVL vector<vector<ll>>
#define VB vector<bool>
#define VVB vector<vector<bool>>
#define PAIR pair<int,int>
#define MP make_pair
#define VP vector<pair<int,int>>
#define VS vector<string>
#define MAP map<int,int>
#define QUE queue<int>
#define DEQ deque<int>
#define PQUE priority_queue<int> //5,5,4,3,3,2,...
#define REPQUE priority_queue<int, vector<int>, greater<int>> //1,1,2,3,4,4,5,...
#define SUM(obj) accumulate((obj).begin(), (obj).end(), 0)
#define SORT(obj) sort((obj).begin(), (obj).end()) // 1,2,3,4,5...
#define RESORT(obj) sort((obj).begin(), (obj).end(), greater<int>()) // 5,4,3,2,1...
#define UB(obj,n) upper_bound((obj).begin(), (obj).end(), n) //itr > n
#define LB(obj,n) lower_bound((obj).begin(), (obj).end(), n) //itr>= n

const ll MOD = (ll)1e9 + 7;
const ll INF = (ll)1e17;

int gcd(int a, int b) {
	if (a == 0 || b == 0) return 0;
	if (a < b) swap(a, b);
	while (b != 0) {
		a = a%b;
		swap(a, b);
	}
	return a;
}

int lcm(int a, int b) {
	if (a == 0 || b == 0) return 0;
	return a / gcd(a, b)*b;
}

vector<bool> Eratosthenes(int N) {
	vector<bool> Eratosthenes(N + 1,true);
	Eratosthenes[0] = false;
	if (N == 0) return Eratosthenes;
	Eratosthenes[1] = false;
	for (int i = 1; i*i <= N; i++) if (Eratosthenes[i]) for (int j = 2 * i; j <= N; j += i) Eratosthenes[j] = false;
	return Eratosthenes;
}

bool pcheck(int N) {
	if (N == 0 || N == 1) return false;
	for (int i = 2; i*i <= N; i++) if (N % i == 0) return false;
	return true;
}

//vector including modulus of N!
vector<ll> factorial(ll N, ll quotient) {
	vector<ll> factorial(N + 1, 1);
	for (ll i = 1; i <= N; i++) {
		factorial[i] *=factorial[i - 1]*i;
		factorial[i] %= quotient;
	}
	return factorial;
}

//repeat square method y = x^n mod quotient 
ll rsm(ll x,ll n,ll quotient){
	ll y = 1;
	while (n > 0) {
		if ((n & 1) == 1) {
			y *= x;
			y %= quotient;
		}
		x *= x;
		x %= quotient;
		n >>= 1; 
	}
	return y;
}

//union-find---------------------------------------------------
int node[10];

int root(int n) {
	if (node[n] == n) return n;
	else return node[n] = root(node[n]);
}

void unite(int n, int m) {
	if (n > m) swap(n, m);
	n = root(n);
	m = root(m);
	if (n == m) return;
	else node[m] = n;
}
//-------------------------------------------------------------

void ANS(bool flag){
	cout << ((flag) ? "YES" : "NO") << endl;
}

void Ans(bool flag) {
	cout << ((flag) ? "Yes" : "No") << endl;
}

void ans(bool flag) {
	cout << ((flag) ? "yes" : "no") << endl;
}

int main() {
	ll H, W, A, B;
	cin >> H >> W >> A >> B;
	vector<ll> f = factorial(200000, MOD);
	ll sum = 0;
	for(ll i = 1; i <= H - A; i++){
		ll nCkl, nCkr;
		ll nl = i - 1 + B - 1;
		ll kl = i - 1;
		ll nr = H - i + W - B - 1;
		ll kr = H - i;
		nCkl = (f[nl] % MOD);
		nCkl *= rsm(f[kl], MOD - 2, MOD);
		nCkl %= MOD;
		nCkl *= rsm(f[nl - kl], MOD - 2, MOD);
		nCkl %= MOD;

		nCkr = (f[nr] % MOD);
		nCkr *= rsm(f[kr], MOD - 2, MOD);
		nCkr %= MOD;
		nCkr *= rsm(f[nr - kr], MOD - 2, MOD);
		nCkr %= MOD;
		
		sum += (nCkl*nCkr) % MOD;
		sum %= MOD;
	}
	cout << sum << endl;
	return 0;
}


Measured memory_bytes: 1792