#include <bits/stdc++.h>

using namespace std;

using Int = int;

struct ModInt {
    static constexpr Int mod = 1e9 + 7;
    Int v;

    ModInt(long long _v = 0) : v(set(_v)) {}
    ModInt(const ModInt &r) : v(set(r.v)) {}

    inline static Int set(const auto x) { return x < 0 ? (x % mod) + mod : x % mod; }
    inline void set() { v = set(v); }

    bool operator<(ModInt r) const { return v < r.v; }
    bool operator>(ModInt r) const { return r.v < v; }
    bool operator==(ModInt r) const { return v == r.v; }
    bool operator!= (ModInt r) const { return v != r.v; }

    ModInt operator-() const { return ModInt(v ? mod - v : v); }
    ModInt &operator=(const ModInt &r) { if (this != &r) v = set(r.v); return *this; }
    ModInt &operator+=(ModInt r) { (v += r.v) %= mod; return *this; }
    ModInt &operator-=(ModInt r) { (v -= r.v - mod) %= mod; return *this; }
    // ModInt &operator*=(ModInt r) { v = (__uint128_t(v) * r.v) % mod; return *this; }
    ModInt &operator*=(ModInt r) { v = 1ULL * v * r.v % mod; return *this; }
    ModInt &operator/=(ModInt r) { *this *= r.inv(); return *this; }
    ModInt operator+(ModInt r) const { return ModInt(*this) += r; }
    ModInt operator-(ModInt r) const { return ModInt(*this) -= r; }
    ModInt operator*(ModInt r) const { return ModInt(*this) *= r; }
    ModInt operator/(ModInt r) const { return ModInt(*this) /= r; }

    ModInt inv() const {
        long long a = v, b = mod, u = 1, w = 0;
        while (b) {
            long long t = a / b;
            std::swap(a -= t * b, b);
            std::swap(u -= t * w, w);
        }
        return ModInt(u);
    }

    ModInt pow(Int e) {
        ModInt a = *this, x(1);
        for ( ; 0 < e; e >>= 1) { if (e & 1) x *= a; a *= a; }
        return x;
    }
    inline ModInt pow(ModInt &e) { return pow(e.v); }
};
std::ostream &operator<<(std::ostream &os, const ModInt &r) { return os << r.v; }
std::istream &operator>>(std::istream &is, ModInt &r) { is >> r.v; r.set();return is; }

ModInt pow(const Int p, const Int e) { return ModInt(p).pow(e); }
std::vector<ModInt> Inverse(const Int n = ModInt::mod - 1) {
    constexpr Int mod = ModInt::mod;
    std::vector<ModInt> inv(n + 1);
    inv[1].v = 1;
    for (Int a = 2; a <= n; ++a)
        inv[a] = inv[mod % a] * ModInt(mod - mod / a);
    return inv;
}

struct Combination {
    const Int mod = ModInt::mod, N;
    std::vector<ModInt> fact, inv_f;

    // MultiChoose を使用する場合は N = 2 * _n とする
    Combination(int _n) : N(_n < mod ? _n : mod - 1), fact(N + 1), inv_f(N + 1) {
        fact[0] = 1;
        for (int i = 1; i <= N; ++i) fact[i] = fact[i - 1] * i;
        inv_f[N] = fact[N].inv();
        for (int i = N; 1 <= i; --i) inv_f[i - 1] = inv_f[i] * i;
    }

    ModInt Choose(const int n, const int k) const {
        if (n < 0 || k < 0 || n < k) return ModInt(0);
        else return fact[n] * inv_f[k] * inv_f[n - k];
    }
};

int main() {
    cin.tie(0); ios::sync_with_stdio(false);

    int h, w, a, b;
    cin >> h >> w >> a >> b;

    Combination cm(h + w + 10);
    ModInt res(0);
    for (int i = 1; i + a <= h; ++i)
        res += cm.Choose(b + i - 2, i - 1) * cm.Choose(w + h - b - i - 1, h - i);

    cout << res.v << endl;

    return 0;
}


Measured memory_bytes: 1920