#include <bits/stdc++.h>
#define err(args...) {}
#ifdef DEBUG
#include "_debug.cpp"
#endif
using namespace std;
using ll = long long;
template <typename T> using lim = numeric_limits<T>;
template <typename T> void fpow_eq(T& x, ll y, T identity = 1) {
    for(; y > 0; x *= x, y >>= 1) {
        if(y & 1) {
            identity *= x;
        }
    }
    x = identity;
}
template <typename T> T fpow(T x, ll y, T identity = 1) {
    T xcopy = x;
    fpow_eq(xcopy, y, identity);
    return xcopy;
}
template <typename signature> using f = const function<signature>&;
template <typename T> void factorize(T n, f<void(T)> each_divisor, f<void(T)> each_prime = [](T) {}) {
    for(T i = 2; i * i <= n; i++) {
        if(n % i == 0) {
            each_prime(i);
            while(n % i == 0) {
                each_divisor(i);
                n /= i;
            }
        }
    }
    if(n > 1) {
        each_divisor(n);
        each_prime(n);
    }
}
template <typename T>
T phi(T n) {
    T ans = n;
    factorize<T>(n, [](T) {}, [&](T p) { ans -= ans / p; });
    return ans;
}
#ifndef __MODINT_INCLUDED_
#define __MODINT_INCLUDED_
// WARNING: use with caution; significant constant factor slowdown
int M, PHI_M;
void set_M(int m) {
    M = m, PHI_M = phi(m);
}
struct modint {
    int val;
    modint() : val(0) {}
    modint(int val) : val(val % M) { val += val < 0 ? M : 0; }
    modint(long long val) : modint(int(val % M)) {}
    modint(const modint& m) : val(m.val) {}
    explicit operator int() const { return val; }
    bool operator==(const modint& y) const { return val == y.val; }
    bool operator!=(const modint& y) const { return val != y.val; }
    bool operator< (const modint& y) const { return val <  y.val; }
    bool operator<=(const modint& y) const { return val <= y.val; }
    bool operator> (const modint& y) const { return val >  y.val; }
    bool operator>=(const modint& y) const { return val >= y.val; }
    modint& operator=(const modint& y) { val = y.val; return *this; }
    modint& operator+=(const modint& y) { val += y.val; val -= val >= M ? M : 0; return *this; }
    modint& operator-=(const modint& y) { val -= y.val; val += val <  0 ? M : 0; return *this; }
    modint& operator*=(const modint& y) { val = ll(val) * y.val % M; return *this; }
    modint& operator/=(const modint& y) { val = ll(val) * fpow(y, PHI_M - 1).val % M; return *this; }
    modint& operator^=(ll y) { fpow_eq(*this, y); return *this; }
    modint operator+(const modint& y) const { return modint(val) += y; }
    modint operator-(const modint& y) const { return modint(val) -= y; }
    modint operator*(const modint& y) const { return modint(val) *= y; }
    modint operator/(const modint& y) const { return modint(val) /= y; }
    modint operator^(ll y) const { return modint(val) ^= y; }
    modint operator-() const { return modint(0) -= *this; }
    modint operator~() const { return modint(1) /= *this; }
    modint& operator++() { val = val == M - 1 ? 0 : val + 1; return *this; }
    modint& operator--() { val = val == 0 ? M - 1 : val - 1; return *this; }
    modint operator++(int) { modint m = *this; ++(*this); return m; }
    modint operator--(int) { modint m = *this; --(*this); return m; }
};
ostream& operator<<(ostream& os, const modint& m) { return os << m.val; }
istream& operator>>(istream& is, modint& m) { is >> m.val; m.val %= M; return is; }
bool operator==(long long x, const modint& y) { return modint((x + M) % M) == y; }
bool operator!=(long long x, const modint& y) { return modint((x + M) % M) != y; }
bool operator< (long long x, const modint& y) { return modint((x + M) % M) <  y; }
bool operator<=(long long x, const modint& y) { return modint((x + M) % M) <= y; }
bool operator> (long long x, const modint& y) { return modint((x + M) % M) >  y; }
bool operator>=(long long x, const modint& y) { return modint((x + M) % M) >= y; }
modint operator+(long long x, const modint& y) { return modint((x + M) % M) + y; }
modint operator*(long long x, const modint& y) { return modint((x + M) % M) * y; }
modint operator-(long long x, const modint& y) { return modint((x + M) % M) - y; }
modint operator/(long long x, const modint& y) { return modint((x + M) % M) / y; }
#endif
#ifndef __PERMUTATIONS_INCLUDED_
#define __PERMUTATIONS_INCLUDED_
modint fact(int n) {
    static vector<modint> fac = {1};
    while(fac.size() <= n) {
        fac.push_back(fac.back() * int(fac.size()));
    }
    return fac[n];
}
modint fact_inv(int n) {
    static vector<modint> inv_fac = {1};
    while(inv_fac.size() <= n) {
        inv_fac.push_back(inv_fac.back() / int(inv_fac.size()));
    }
    return inv_fac[n];
}
#endif
#ifndef __COMBINATIONS_INCLUDED_
#define __COMBINATIONS_INCLUDED_
modint C(int n, int k) {
    return fact(n) * fact_inv(k) * fact_inv(n - k);
}
#endif
modint walk(int R, int D) {
    return C(R + D, D);
}
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    set_M(1'000'000'007);
    int h, w, a, b;
    cin >> h >> w >> a >> b;
    modint ans = 0;
    for(int i = 0; i <= h - 1 - a; i++) {
        ans += walk(b - 1, i) * walk(w - 1 - b, h - 1 - i);
    }
    cout << ans << endl;
    return 0;
}


Measured memory_bytes: 1784