// Original C++ solution (slower):
#include<bits/stdc++.h>

using namespace std;



typedef long long LL;



const int N = 3e5;

const LL MOD = 1e9+7;



inline LL dmod(LL x){

	return x%MOD;

}



LL fakto[N+5];



void pre(){

	fakto[0] = 1LL;

	for(int i=1;i<=N;i++){

		fakto[i] = dmod(fakto[i-1]*(LL)(i));

	}

	return;

}



LL fe(LL x, LL y){

	if(y==0) return 1LL;

	LL ret = fe(x,y/2);

	ret = dmod(ret*ret);

	if(y&1){

		ret = dmod(ret*x);

	}

	return ret;

}



LL nCr(LL x, LL y){

	LL tmp = dmod(fakto[y]*fakto[x-y]);

	tmp = fe(tmp,MOD-2);

	tmp = dmod(tmp*fakto[x]);

	return tmp;

}



LL step(int x, int y, int a, int b){

	int dx = a-x;

	int dy = b-y;

	int tot = dx+dy;

	return nCr(tot,dx);

}



int h,w,a,b;

int main(){

	pre();

	cin >> h >> w >> a >> b;

	LL ret = 0LL;

	for(int i=1;i<=h-a;i++){

		LL tmp = step(1,1,i,b);

		tmp = dmod(tmp*step(i,b+1,h,w));

		ret = dmod(ret+tmp);

	}

	cout << ret << endl;

	return 0;

}

// Optimized solution to the same problem (faster):
// #pragma GCC optimize("Ofast,O3,unroll-loops")

// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")



#include <vector>

#include <list>

#include <map>

#include <set>

#include <deque>

#include <queue>

#include <stack>

#include <bitset>

#include <algorithm>

#include <functional>

#include <numeric>

#include <utility>

#include <iostream>

#include <sstream>

#include <iomanip>

#include <cstdio>

#include <cmath>

#include <cstdlib>

#include <cctype>

#include <string>

#include <cstring>

#include <cstdio>

#include <cmath>

#include <cstdlib>

#include <ctime>

#include <climits>

#include <complex>

#include <ext/pb_ds/assoc_container.hpp>

#include <ext/pb_ds/tree_policy.hpp>



using namespace __gnu_pbds;

using namespace std;



#define endl '\n'

#define hoise cerr<<"hoise - "<<__LINE__<<"\n"

#define tham getchar()

#define set0(ar) memset(ar, 0, sizeof ar)

#define setinf(ar) memset(ar, 126, sizeof ar)

#define vsort(v) sort(v.begin(), v.end())

#define all(x) (x).begin(), (x).end()

#define FASTIO ios::sync_with_stdio(false);cin.tie(nullptr);



using ll = long long;

using pii = pair <int, int>;

using pll = pair <ll, ll>;

using vi = vector <int>;

using vl = vector <ll>;

using vpii = vector < pii >;

using vpll = vector < pll >;



const int MXN = (int)2e5+6;

const double PI = acos(-1.0);

const ll MOD = 1e9 + 7;

const int INF = 1e9;

const double EPS = 1e-6;

const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1};



#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args); }

void err(istream_iterator<string> it) {}

template<typename T, typename... Args>

void err(istream_iterator<string> it, T a, Args... args) {

    cerr << *it << " = " << a << endl;

    err(++it, args...);

}



int flipBit (int mask, int k) { return mask = mask ^ (1 << k); }

bool checkBit (int mask, int k) { return (mask >> k) & 1; }

int setBit (int mask, int k) { return mask = mask | (1 << k); }

int resetBit (int mask, int k) { if (checkBit (mask, k)) { mask = flipBit (mask, k); } return mask; }



inline void normal(ll &a) { a %= MOD; (a < 0) && (a += MOD); }

inline ll modMul(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); return (a * b) % MOD; }

inline ll modAdd(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); return (a + b) % MOD; }

inline ll modSub(ll a, ll b) { a %= MOD, b %= MOD; normal(a), normal(b); a -= b; normal(a); return a; }

inline ll modPow(ll b, ll p) { ll r = 1; while (p) { if (p & 1) r = modMul(r, b); b = modMul(b, b); p >>= 1; } return r; }

inline ll modInverse(ll a) { return modPow(a, MOD - 2); }

inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }



template <typename T> using orderedSet = tree<T, null_type, greater<T>, rb_tree_tag, tree_order_statistics_node_update>;

template <typename T> using orderedSet1 = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;



bool approximatelyEqual(float a, float b, float epsilon) {

    return fabs(a - b) <= ( (fabs(a) < fabs(b) ? fabs(b) : fabs(a)) * epsilon);

}

bool essentiallyEqual(float a, float b, float epsilon) {

    return fabs(a - b) <= ( (fabs(a) > fabs(b) ? fabs(b) : fabs(a)) * epsilon);

}

bool definitelyGreaterThan(float a, float b, float epsilon) {

    return (a - b) > ( (fabs(a) < fabs(b) ? fabs(b) : fabs(a)) * epsilon);

}

bool definitelyLessThan(float a, float b, float epsilon) {

    return (b - a) > ( (fabs(a) < fabs(b) ? fabs(b) : fabs(a)) * epsilon);

}



/*--------------------------------------------------------------------------------------------------------------------------*/



ll fact[MXN], inv[MXN];



ll ncr (ll n, ll r) {

	return (fact[n] % MOD * inv[n - r] % MOD * inv[r] % MOD) % MOD;

}



void solve () {

	

	ll h, w, a, b;

	cin >> h >> w >> a >> b;

	

	fact[0] = 1;

	for (int i = 1; i <= h + w; ++i) {

		fact[i] = fact[i - 1] * i;

		fact[i] %= MOD;

	}

	

	for (int i = 0; i <= h + w; ++i) {

		inv[i] = modInverse (fact[i]);

		inv[i] %= MOD;

	}

	

	ll ans = 0;

	

	for (int i = b; i < w; ++i) {

		ll comb1 = ncr (h + i - a - 1, i);

		ll comb2 = ncr (w + a - i - 2, a - 1);

		ans += comb1 * comb2;

		ans %= MOD;

	}

	cout << ans << endl;

}



int main(){

	// FASTIO

	

	int t;

	// cin >> t;

	t = 1;

	

	while (t--) {

		solve ();

	}

	

    return 0;

}



/*

 * be careful before submitting in Lightoj, SPOJ, UVA

*/


// Fastest known solution for this problem: