// Original C++ solution (slower):
//#pragma GCC optimize(2)





#include<bits/stdc++.h>

using namespace std;

/*#include<ext/pb_ds/assoc_container.hpp>

#include<ext/pb_ds/tree_policy.hpp>

#include<ext/pb_ds/hash_policy.hpp>

#include<ext/pb_ds/trie_policy.hpp>

#include<ext/pb_ds/priority_queue.hpp>

#include<ext/rope>*/

//using namespace __gnu_cxx;

//using namespace __gnu_pbds;

//void err(istream_iterator<string> it){cerr<<endl;}

//template<typename T, typename... Args>void err(istream_iterator<string> it, T a, Args... args){cerr << *it << " = " << a << " , ";err(++it, args...);}

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

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

#define fpre(x) cout<<fixed<<setprecision(x)

#define clr(v) (v).clear()

#define pii pair<int,int>

#define pdd pair<double,double>

#define pli pair<ll,int>

#define pll pair<ll,ll>

#define mp make_pair

#define eb emplace_back

#define pb emplace_back

#define ll long long

#define ld long double

#define ull unsigned long long

#define uint unsigned int

#define ushort unsigned short

#define IOS ios::sync_with_stdio(0);cin.tie(0);cout.tie(0)

#define lowbit(i) (i&(-i))

#define lson rt<<1

#define rson lson|1

#define fi first

#define se second

const double eps=1e-7;

const double pi=acos(-1);

inline int dcmp(double x)

{

    if(x<-eps)

        return -1;

    if(x>eps)

        return 1;

    return 0;

}

//-----------------------------------------------head



const int maxn=2e5+5;

const ll mod=1e9+7;

ll f[maxn+5],invf[maxn+5];

ll qp(ll x,ll n)

{

    x%=mod;

    ll r=1;

    while(n)

    {

        if(n&1)

            r=r*x%mod;

        x=x*x%mod;

        n>>=1;

    }

    return r;

}

void init()

{

    f[0]=1;

    for(int i=1;i<=maxn;++i)

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

    invf[maxn]=qp(f[maxn],mod-2);

    for(int i=maxn-1;~i;--i)

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

}

ll c(int n,int m)

{

    return f[n]*(invf[m]*invf[n-m]%mod)%mod;

}

int main()

{

    init();

    int h,w,a,b;

    while(~scanf("%d%d%d%d",&h,&w,&a,&b))

    {

        ll r=0;

        for(ll i=b+1;i<=w;++i)

        {

            ll tmp=c(h-a+i-2,h-a-1)*c(w-i+a-1,w-i)%mod;

            r=(r+tmp)%mod;

        }

        printf("%lld\n",r);

    }

}



/*

















































*/
















// 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: