#include<bits/stdc++.h>

using namespace std;

#define int long long
#define ar array
#define vt vector
#define pb push_back
#define all(c) (c).begin(), (c).end()
#define sz(x) (int)(x).size()

#define F_OR(i, a, b, s) for (int i=(a); (s)>0?i<(b):i>(b); i+=(s))
#define F_OR1(e) F_OR(i, 0, e, 1)
#define F_OR2(i, e) F_OR(i, 0, e, 1)
#define F_OR3(i, b, e) F_OR(i, b, e, 1)
#define F_OR4(i, b, e, s) F_OR(i, b, e, s)
#define GET5(a, b, c, d, e, ...) e
#define F_ORC(...) GET5(__VA_ARGS__, F_OR4, F_OR3, F_OR2, F_OR1)
#define FOR(...) F_ORC(__VA_ARGS__)(__VA_ARGS__)
#define EACH(x, a) for (auto& x: a)

template<class T>
bool umin(T &a, const T &b) {
    return b < a ? a = b, 1 : 0;
}

template<class T>
bool umax(T &a, const T &b) {
    return a < b ? a = b, 1 : 0;
}

template<class A>
void read(vt<A> &v);

template<class A, size_t S>
void read(ar<A, S> &a);

template<class T>
void read(T &x) {
    cin >> x;
}

void read(double &d) {
    string t;
    read(t);
    d = stod(t);
}

void read(long double &d) {
    string t;
    read(t);
    d = stold(t);
}

template<class H, class... T>
void read(H &h, T &... t) {
    read(h);
    read(t...);
}

template<class A>
void read(vt<A> &x) {
    EACH(a, x)read(a);
}

template<class A, size_t S>
void read(array<A, S> &x) {
    EACH(a, x)read(a);
}

string to_string(char c) {
    return string(1, c);
}

string to_string(bool b) {
    return b ? "true" : "false";
}

string to_string(const char *s) {
    return string(s);
}

string to_string(string s) {
    return s;
}

string to_string(vt<bool> v) {
    string res;
    FOR(sz(v))res += char('0' + v[i]);
    return res;
}

template<size_t S>
string to_string(bitset<S> b) {
    string res;
    FOR(S)res += char('0' + b[i]);
    return res;
}

template<class T>
string to_string(T v) {
    bool f = 1;
    string res;
    EACH(x, v) {
        if (!f)
            res += ' ';
        f = 0;
        res += to_string(x);
    }
    return res;
}

template<class A>
void write(A x) {
    cout << to_string(x);
}

template<class H, class... T>
void write(const H &h, const T &... t) {
    write(h);
    write(t...);
}

void print() {
    write("\n");
}

template<class H, class... T>
void print(const H &h, const T &... t) {
    write(h);
    if (sizeof...(t))
        write(' ');
    print(t...);
}

template<class T, class U>
void vti(vt<T> &v, U x, size_t n) {
    v = vt<T>(n, x);
}

template<class T, class U>
void vti(vt<T> &v, U x, size_t n, size_t m...) {
    v = vt<T>(n);
    EACH(a, v)vti(a, x, m);
}

const int M = 1e9 + 7, mxN = 2e5;
int h, w, a, b;
int F[mxN + 1];

int modpow(int x, int p) {
    if (!p) return 1;
    int val = modpow(x, p / 2);
    val = (val * val) % M;
    if (p & 1) val = (val * x) % M;
    return val;
}

int inverse(int x) {
    int val = modpow(x, M - 2);
    return val;
}

int ncr(int n, int r) {
    if (n < r) return 0;
    int x = (F[n - r] * F[r]) % M;
    x = (F[n] * inverse(x)) % M;
    return x;
}

/*
 * h and w are row and column
 * let the indexing start at 0
 *
 * nof ways of reaching from
 * 0,0 to 0,b-1
 * 0,0 to 1,b-1
 * .
 * .
 * .
 * 0,0 to h-a-1,b-1
 *
 * 0,b to h-1,w-1
 * .
 * .
 * .
 * .h-a-1,b to h-1,w-1
 */

void solve() {
    read(h, w, a, b);
    
    F[1] = 1;
    F[0] = 1;
    FOR(i, 2, mxN + 1) {
        F[i] = (F[i-1] * i) % M;
    }
    vt<int> f(h - a);
    FOR(h - a) {
        int x = (b - 1);
        int y = i;
        f[i] = ncr(x + y, x);
    }
    
    int ans = 0;
    
    FOR(h - a) {
        int x = (w - b - 1);
        int y = (h - i - 1);
        
        int val = ncr(x + y, x);
        val = (val * f[i]) % M;
        ans = (ans + val) % M;
    }
    print(ans);
}

int32_t main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    
    int tt = 1;
    //read(tt);
    FOR(tt) {
        //write("Case #", i + 1, ": ");
        solve();
        
    }
    
}


Measured memory_bytes: 5552