#include <bits/stdc++.h>
#define SORT(a) sort(a.begin(), a.end())
#define RSORT(a) sort(a.rbegin(), a.rend())
#define REP(i, n) for (int i = 0; i < n; i++)
#define RREP(i, n) for (int i = n - 1; 0 <= i; i--)
#define FOR(i, start, end) for (int i = start; i < end; i++)
#define RFOR(i, start, end) for (int i = start - 1; 0 <= i; i--)
#define ALL(a) a.begin(), a.end()
using ll = long long;
using namespace std;
constexpr int INF32       = 1'050'000'000;
constexpr long long INF64 = 4'000'000'000'000'000'000;
constexpr int MOD7        = 1'000'000'007;
constexpr int MOD9        = 1'000'000'009;
template <class T> inline bool chmin(T &a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T> inline bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
void print() { std::cout << '\n'; }
template <class H, class... T> void print(H &&head, T &&... args) {
    std::cout << head;
    sizeof...(args) == 0 ? std::cout << "" : std::cout << ' ';
    print(std::forward<T>(args)...);
}
template <class T> void print(std::vector<T> &v) {
    for (int i = 0; i < v.size(); i++) {
        std::cout << v[i];
        i == v.size() - 1 ? std::cout << '\n' : std::cout << ' ';
    }
}
template <class T> void print(std::vector<std::vector<T>> &v) {
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++) {
            std::cout << v[i][j];
            j == v[i].size() - 1 ? std::cout << '\n' : std::cout << ' ';
        }
    }
}
void debug() { std::cerr << '\n'; }
template <class H, class... T> void debug(H &&head, T &&... args) {
    std::cerr << head;
    sizeof...(args) == 0 ? std::cerr << "" : std::cerr << ' ';
    debug(std::forward<T>(args)...);
}
template <class T> void debug(std::vector<T> &v) {
    for (int i = 0; i < v.size(); i++) {
        std::cerr << v[i];
        i == v.size() - 1 ? std::cerr << '\n' : std::cerr << ' ';
    }
}
template <class T> void debug(std::vector<std::vector<T>> &v) {
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++) {
            std::cerr << v[i][j];
            j == v[i].size() - 1 ? std::cerr << '\n' : std::cerr << ' ';
        }
    }
}

template <int mod> class modint {
  private:
    long long val;

  public:
    constexpr modint(long long x = 0) noexcept : val(x % mod) {
        if (val < 0)
            val += mod;
    };
    constexpr modint operator-() const noexcept { return val ? mod - val : 0; }
    constexpr modint operator+(const modint &x) const noexcept {
        return modint(*this) += x;
    }
    constexpr modint &operator++() noexcept {
        val += 1;
        if (mod <= val)
            val -= mod;
        return *this;
    }
    constexpr modint operator++(int) noexcept {
        modint<mod> ret = *this;
        val += 1;
        if (mod <= val)
            val -= mod;
        return ret;
    }
    constexpr modint operator-(const modint &x) const noexcept {
        return modint(*this) -= x;
    }
    constexpr modint &operator--() noexcept {
        val -= 1;
        if (val < 0)
            val += mod;
        return *this;
    }
    constexpr modint operator--(int) noexcept {
        modint<mod> ret = *this;
        val -= 1;
        if (val < 0)
            val += mod;
        return ret;
    }
    constexpr modint operator*(const modint &x) const noexcept {
        return modint(*this) *= x;
    }
    constexpr modint operator/(const modint &x) const noexcept {
        return modint(*this) /= x;
    }
    constexpr modint &operator+=(const modint &x) noexcept {
        val += x.val;
        if (mod <= val)
            val -= mod;
        return *this;
    }
    constexpr modint &operator-=(const modint &x) noexcept {
        val -= x.val;
        if (val < 0)
            val += mod;
        return *this;
    }
    constexpr modint &operator*=(const modint &x) noexcept {
        val = val * x.val % mod;
        return *this;
    }
    constexpr modint &operator/=(const modint &x) noexcept {
        val *= x.inv();
        return *this;
    }
    constexpr modint inv() const noexcept {
        long long a = val, b = mod, u = 1, v = 0, t;
        while (0 < b) {
            t = a / b;
            a -= t * b;
            swap(a, b);
            u -= t * v;
            swap(u, v);
        }
        return modint(u);
    }
    constexpr bool operator==(const modint &x) const noexcept {
        return this->val == x.val;
    }
    constexpr bool operator!=(const modint &x) const noexcept {
        return this->val != x.val;
    }
    constexpr bool operator<(const modint &x) const noexcept {
        return val < x.val;
    }
    constexpr bool operator<=(const modint &x) const noexcept {
        return val <= x.val;
    }
    constexpr bool operator>(const modint &x) const noexcept {
        return x.val < val;
    }
    constexpr bool operator>=(const modint &x) const noexcept {
        return x.val <= val;
    }
    friend constexpr ostream &operator<<(ostream &os, modint<mod> &x) noexcept {
        return os << x.val;
    }
    friend constexpr istream &operator>>(istream &is, modint<mod> &x) noexcept {
        return is >> x.val;
    }
    friend constexpr modint<mod> pow(const modint<mod> &radix,
                                     long long x) noexcept {
        if (x == 0)
            return 1;
        auto t = pow(radix, x / 2);
        t      = t * t;
        if (x & 1)
            t = t * radix;
        return t;
    }
};

using mint = modint<MOD7>;

template <int mod> class nCr {
  private:
    constexpr static int MAX_SIZE = 1000000;
    vector<long long> fac, fnv, inv;
    constexpr void init() noexcept {
        inv[0] = 0;
        for (int i = 2; i < MAX_SIZE; ++i) {
            fac[i] = fac[i - 1] * i % mod;
            inv[i] = mod - inv[mod % i] * (mod / i) % mod;
            fnv[i] = fnv[i - 1] * inv[i] % mod;
        }
    }

  public:
    constexpr nCr() noexcept
        : fac(MAX_SIZE, 1), fnv(MAX_SIZE, 1), inv(MAX_SIZE, 1) {
        init();
    }

    constexpr long long cal(int n, int r) {
        if (n < r || n < 0 || r < 0)
            return 0;
        return fac[n] * (fnv[r] * fnv[n - r] % mod) % mod;
    }
};

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

    int H, W, A, B;
    cin >> H >> W >> A >> B;
    auto ncr = nCr<MOD7>();
    mint ans = 0;
    FOR(i, B + 1, W + 1) {
        int h    = H - A - 1;
        int w    = i - 1;
        mint sum = ncr.cal(h + w, w);
        h        = A - 1;
        w        = W - i;
        sum *= ncr.cal(h + w, w);
        ans += sum;
    }
    print(ans);

    return 0;
}

Measured memory_bytes: 23680