// Slower C++ solution:
#include<bits/stdc++.h>

#define int long long

#define rg register

#define file(x) freopen(x".in","r",stdin);freopen(x".out","w",stdout);

using namespace std;

const int N=200000+10;

const int mod=1e9+7;

int read(){

    int x=0,f=1;char c=getchar();

    while(c<'0'||c>'9') f=(c=='-')?-1:1,c=getchar();

    while(c>='0'&&c<='9') x=x*10+c-48,c=getchar();

    return f*x;

}

int inv[N],jc[N];

int ksm(int a,int b){

	int ans=1;

	while(b){

		if(b&1) ans=ans*a%mod;

		a=a*a%mod;

		b>>=1;

	}

	return ans;

}

int C(int n,int m){

	return jc[n]*inv[m]%mod*inv[n-m]%mod;

}

int calc(int x,int y,int X,int Y){

	int n=abs(X-x),m=abs(Y-y);

	return C(n+m,n);

}

main(){

    //file("");

	jc[0]=1;

	for(int i=1;i<=N-10;i++)

		jc[i]=jc[i-1]*i%mod;

	inv[N-10]=ksm(jc[N-10],mod-2);

	for(int i=N-11;i>=0;i--)

		inv[i]=inv[i+1]*(i+1)%mod;

	int H=read(),W=read(),A=read(),B=read(),ans=calc(1,1,H,W);

	for(int i=H-A+1;i<=H;i++)

		ans=(ans-calc(1,1,i,B)*calc(i,B+1,H,W)%mod+mod)%mod;

	cout<<ans;

    return 0;

}


// Faster C++ solution for the same problem (measured speedup: 4.225800516259539x):
#include <stdio.h>

#include <iostream>

#include <algorithm>

#include <queue>

#include <cstring>

#include <string>

#include <stack>

#include <map>

#include <set>

#include <cmath>

#include <iomanip>

using namespace std;



#define pb push_back

#define All(a) a.begin(), a.end()

#define met(a, b) memset(a, b, sizeof(a))

#define rep1(i, l, r) for(int i = l; i <= r; ++i)

#define rep2(i, l, r) for(int i = l; i < r; ++i) 

#define per(i, r, l) for(int i = r; i >= l; --i)

typedef long long ll;

typedef double db;

typedef long double ldb;

const int NIL = -1;

const int oo = 0x3f3f3f3f;

const ll INF = 2e18;

const db eps = 1e-8;

const db PI = acos(-1.0);

const int maxn = 2e5 + 7;

const int mod = 1e9 + 7;



struct node

{

	int x, y;

	node(int a, int b):x(a), y(b){}

};



ll C1[maxn], C2[maxn];



inline int read(void)

{

	int x = 0, f = 1; char ch = getchar();

	while(ch < '0' || ch > '9')	{ if(ch == '-') f = -1; ch = getchar(); } 

	while(ch >= '0' && ch <= '9') {	x = (x << 1) + (x << 3) + ch - '0';	ch = getchar();	}

	return x * f;

}



inline void write(ll x)

{

	if(x < 0) { putchar('-'); x = -x; }

    if(x>=10) write(x/10); 

	putchar(x%10+'0'); 

}



ll find(ll a, ll b)

{

	if(a == 1) return 1;

	ll ans = b / a + 1;

	ans = ans * find(a*ans-b, b) % b;

	return ans;

}



int main(void)

{

	int n = read(), m = read(), a = read(), b = read();

	node begin(1, 1), mid(n-a, b+1), end(n, m);

	C1[0] = C2[0] = 1;

	int n1 = n-a-1+b, n2 = a+m-b-1;

	C1[n1] = C2[n2] = 1;

	rep1(i, 1, n1/2) C1[n1-i] = C1[i] = C1[i-1] * (n1 - i + 1) % mod * find(i, mod) % mod;

	rep1(i, 1, n2/2) C2[n2-i] = C2[i] = C2[i-1] * (n2 - i + 1) % mod * find(i, mod) % mod;

//	if((n1&1)== 0) cout<<C1[n1/2-1]<<" "<<C1[n1/2]<<" "<<C1[n1/2+1]<<endl;

//	else cout<<C1[n1/2]<<" "<<C1[n1/2+1]<<endl;

//	if((n2&1) == 0) cout<<C2[n2/2-1]<<" "<<C2[n2/2]<<" "<<C2[n2/2+1]<<endl;

//	else cout<<C2[n2/2]<<" "<<C2[n2/2+1]<<endl;

	ll ans = 0;

	while(mid.x > 0 && mid.y <= m)

	{

		ans = (ans + C1[mid.y-1] * C2[end.y-mid.y] % mod) % mod;

		--mid.x;

		++mid.y;

	}

	cout<<ans;

	

	return 0;

}