#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MOD = 1e9 + 7;

// MODULAR INTEGER - Start of snippet
template<const int &MOD>
struct _m_int {
    int val;
    /*
    ** MODULAR INTEGER TEMPATE - credited to Neal Wu
    */
    _m_int(long long v = 0) {
        if (v < 0) v = v % MOD + MOD;
        if (v >= MOD) v %= MOD;
        val = int(v);
    }
 
    _m_int(uint64_t v) {
        if (v >= MOD) v %= MOD;
        val = int(v);
    }
 
    _m_int(int v) : _m_int((long long) v) {}
    _m_int(unsigned v) : _m_int(uint64_t(v)) {}
 
    static int inv_mod(int a, int m = MOD) {
        // https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm#Example
        int g = m, r = a, x = 0, y = 1;
        while (r != 0) {
            int q = g / r;
            g %= r; swap(g, r);
            x -= q * y; swap(x, y);
        }
        return x < 0 ? x + m : x;
    }
 
    explicit operator int() const { return val; }
    explicit operator unsigned() const { return val; }
    explicit operator long long() const { return val; }
    explicit operator uint64_t() const { return val; }
    explicit operator double() const { return val; }
    explicit operator long double() const { return val; }
 
    _m_int& operator+=(const _m_int &other) {
        val -= MOD - other.val;
        if (val < 0) val += MOD;
        return *this;
    }
 
    _m_int& operator-=(const _m_int &other) {
        val -= other.val;
        if (val < 0) val += MOD;
        return *this;
    }
 
    static unsigned fast_mod(uint64_t x, unsigned m = MOD) {
#if !defined(_WIN32) || defined(_WIN64)
        return unsigned(x % m);
#endif
        // Optimized mod for Codeforces 32-bit machines.
        // x must be less than 2^32 * m for this to work, so that x / m fits in an unsigned 32-bit int.
        unsigned x_high = unsigned(x >> 32), x_low = unsigned(x);
        unsigned quot, rem;
        asm("divl %4\n"
            : "=a" (quot), "=d" (rem)
            : "d" (x_high), "a" (x_low), "r" (m));
        return rem;
    }
 
    _m_int& operator*=(const _m_int &other) {
        val = fast_mod(uint64_t(val) * other.val);
        return *this;
    }
 
    _m_int& operator/=(const _m_int &other) {
        return *this *= other.inv();
    }
 
    friend _m_int operator+(const _m_int &a, const _m_int &b) { return _m_int(a) += b; }
    friend _m_int operator-(const _m_int &a, const _m_int &b) { return _m_int(a) -= b; }
    friend _m_int operator*(const _m_int &a, const _m_int &b) { return _m_int(a) *= b; }
    friend _m_int operator/(const _m_int &a, const _m_int &b) { return _m_int(a) /= b; }
 
    _m_int& operator++() {
        val = val == MOD - 1 ? 0 : val + 1;
        return *this;
    }
 
    _m_int& operator--() {
        val = val == 0 ? MOD - 1 : val - 1;
        return *this;
    }
 
    _m_int operator++(int) { _m_int before = *this; ++*this; return before; }
    _m_int operator--(int) { _m_int before = *this; --*this; return before; }
 
    _m_int operator-() const {
        return val == 0 ? 0 : MOD - val;
    }
 
    friend bool operator==(const _m_int &a, const _m_int &b) { return a.val == b.val; }
    friend bool operator!=(const _m_int &a, const _m_int &b) { return a.val != b.val; }
    friend bool operator<(const _m_int &a, const _m_int &b) { return a.val < b.val; }
    friend bool operator>(const _m_int &a, const _m_int &b) { return a.val > b.val; }
    friend bool operator<=(const _m_int &a, const _m_int &b) { return a.val <= b.val; }
    friend bool operator>=(const _m_int &a, const _m_int &b) { return a.val >= b.val; }
 
    _m_int inv() const {
        return inv_mod(val);
    }
 
    _m_int pow(long long p) const {
        if (p < 0)
            return inv().pow(-p);
        _m_int a = *this, result = 1;
        while (p > 0) {
            if (p & 1)
                result *= a;
            p >>= 1;
            if (p > 0)
                a *= a;
        }
        return result;
    }
 
    friend ostream& operator<<(ostream &os, const _m_int &m) {
        return os << m.val;
    }
};
// MODULAR INTEGER - End of snippet
 
using Mint = _m_int<MOD>;

vector<Mint> inv, factorial, inv_factorial;
 
void prepare_factorials(int maximum) {
    // Make sure MOD is prime, which is necessary for the inverse algorithm below.
    for (int p = 2; p * p <= MOD; p += p % 2 + 1)
        assert(MOD % p != 0);
 
    inv = {0, 1};
    factorial = inv_factorial = {1, 1};
 
    maximum = max(maximum, 1);
    inv.resize(maximum + 1);
    factorial.resize(maximum + 1);
    inv_factorial.resize(maximum + 1);
 
    for (int i = 2; i <= maximum; i++) {
        inv[i] = inv[MOD % i] * (MOD - MOD / i);
        factorial[i] = i * factorial[i - 1];
        inv_factorial[i] = inv[i] * inv_factorial[i - 1];
    }
}

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

	int height, width, A, B;
	cin >> height >> width >> A >> B;
	prepare_factorials((int) 5e5 + 5);

	auto ways = [](int h, int w) -> Mint {
		Mint num = factorial[h + w - 2];
		Mint denom = factorial[h - 1] * factorial[w - 1];
		return Mint(num / denom);
	};

	Mint ans = 0;
	for (int row = 0; row < height - A; ++row) {
		Mint toRight = ways(row + 1, B + 1);
		Mint toRB = ways(height - row, (row == height - A - 1 ? width - B : width - B - 1));
		ans += toRight * toRB;
	}

	cout << ans << '\n';

	return 0;
}

Measured memory_bytes: 8976