//header
#define set_header 1
#ifdef set_header
    #pragma GCC optimize("Ofast")
    #include <bits/stdc++.h>
    #ifdef LOCAL
        #include "cxx-prettyprint-master/prettyprint.hpp"
        #define print(x) cout << x << endl
    #else
        #define print(...) 42
    #endif
    using namespace std;
    using ll = long long;
    #define all(x) (x).begin(), (x).end()
    #define reverse(x) (x).rbegin(), (x).rend()
    #define FOR(i,a,b) for(ll i=(a);i<(b);++i)
    #define rep(i,n)  FOR(i,0,n)
    #define SZ(x) ((ll)(x).size())
    #define sum(x) accumulate(ALL(x), 0LL)//?
    #define pb(x) push_back(x)
    typedef pair < ll , ll >P;
    ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
    template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
    template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
    template <std::uint_fast64_t Modulus> class modint {
        using u64 = std::uint_fast64_t;

        public:
        u64 a;

        constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {}
        constexpr u64 &value() noexcept { return a; }
        constexpr const u64 &value() const noexcept { return a; }
        constexpr modint operator+(const modint rhs) const noexcept {
            return modint(*this) += rhs;
        }
        constexpr modint operator-(const modint rhs) const noexcept {
            return modint(*this) -= rhs;
        }
        constexpr modint operator*(const modint rhs) const noexcept {
            return modint(*this) *= rhs;
        }
        constexpr modint operator/(const modint rhs) const noexcept {
            return modint(*this) /= rhs;
        }
        constexpr modint &operator+=(const modint rhs) noexcept {
            a += rhs.a;
            if (a >= Modulus) {
            a -= Modulus;
            }
            return *this;
        }
        constexpr modint &operator-=(const modint rhs) noexcept {
            if (a < rhs.a) {
            a += Modulus;
            }
            a -= rhs.a;
            return *this;
        }
        constexpr modint &operator*=(const modint rhs) noexcept {
            a = a * rhs.a % Modulus;
            return *this;
        }
        constexpr modint &operator/=(modint rhs) noexcept {
            u64 exp = Modulus - 2;
            while (exp) {
            if (exp % 2) {
                *this *= rhs;
            }
            rhs *= rhs;
            exp /= 2;
            }
            return *this;
        }
        };
    template< typename T >
    T mod_pow(T x, T n, const T &p) {
        T ret = 1;
        while(n > 0) {
            if(n & 1) (ret *= x) %= p;
            (x *= x) %= p;
            n >>= 1;
        }
        return ret;
    }
    class range {private: struct I{int x;int operator*(){return x;}bool operator!=(I& lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;
    public:range(int n):i({0}),n({n}){}range(int i,int n):i({i}),n({n}){}I& begin(){return i;}I& end(){return n;}};
    uint64_t my_rand(void) {
	static uint64_t x = 88172645463325252ULL;
	x = x ^ (x << 13); x = x ^ (x >> 7);
	return x = x ^ (x << 17);
}
#endif
//constant
#define INF 1'010'000'000'000'000'017LL
#define mod 1000000007LL
#define eps 0.0001
//library
template< typename T >
struct Combination {
    vector< T > _fact, _rfact, _inv;

    Combination(int sz) : _fact(sz + 1), _rfact(sz + 1), _inv(sz + 1) {
        _fact[0] = _rfact[sz] = _inv[0] = 1;
        for(int i = 1; i <= sz; i++) _fact[i] = _fact[i - 1] * i;
        _rfact[sz] /= _fact[sz];
        for(int i = sz - 1; i >= 0; i--) _rfact[i] = _rfact[i + 1] * (i + 1);
        for(int i = 1; i <= sz; i++) _inv[i] = _rfact[i] * _fact[i - 1];
    }

    inline T fact(int k) const { return _fact[k]; }

    inline T rfact(int k) const { return _rfact[k]; }

    inline T inv(int k) const { return _inv[k]; }

    T P(int n, int r) const {
        if(r < 0 || n < r) return 0;
        return fact(n) * rfact(n - r);
    }

    T C(int p, int q) const {
        if(q < 0 || p < q) return 0;
        return fact(p) * rfact(q) * rfact(p - q);
    }

    T H(int n, int r) const {
        if(n < 0 || r < 0) return (0);
        return r == 0 ? 1 : C(n + r - 1, r);
    }
};
//main
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    ll H, W, A, B;
    cin >> H >> W >> A >> B;
    modint<mod> ans;
    Combination<modint<mod>> comb(H+W); 
    rep(i,H-A){
        ans+=comb.C(B+i-1, i)*comb.C(W-B-1+H-i-1, H-i-1);
    }
    cout << ans.value() << endl;
}


Measured memory_bytes: 4992