// >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define int ll
#define double ld
#define rep(i,n) for (int i = 0; i < (int)(n); i++)
#define rep1(i,n) for (int i = 1; i <= (int)(n); i++)
#define repR(i,n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i,n) for (int i = (int)(n); i >= 1; i--)
#define loop(i,a,B) for (int i = a; i B; i++)
#define loopR(i,a,B) for (int i = a; i B; i--)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fst first
#define snd second
#define INF (numeric_limits<int>::max()/2-1)
#ifdef LOCAL
#include "debug.hpp"
#define dump(...) cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] ", dump_impl(#__VA_ARGS__, __VA_ARGS__)
#define say(x) cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] " << x << endl
#define debug if (1)
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#endif
template <class T> using pque_max = priority_queue<T>;
template <class T> using pque_min = priority_queue<T, vector<T>, greater<T> >;
template <class T, class = typename T::iterator, class = typename enable_if<!is_same<T, string>::value>::type>
ostream& operator<<(ostream& os, T const& v) { bool f = true; for (auto const& x : v) os << (f ? "" : " ") << x, f = false; return os; }
template <class T, class = typename T::iterator, class = typename enable_if<!is_same<T, string>::value>::type>
istream& operator>>(istream& is, T &v) { for (auto& x : v) is >> x; return is; }
template <class T, class S> istream& operator>>(istream& is, pair<T,S>& p) { return is >> p.first >> p.second; }
struct IOSetup { IOSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); } } iosetup;
template <class F> struct FixPoint : private F {
    constexpr FixPoint(F&& f) : F(forward<F>(f)) {}
    template <class... T> constexpr auto operator()(T&&... x) const { return F::operator()(*this, forward<T>(x)...); }
};
struct MakeFixPoint {
    template <class F> constexpr auto operator|(F&& f) const { return FixPoint<F>(forward<F>(f)); }
};
#define MFP MakeFixPoint()|
#define def(name, ...) auto name = MFP [&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
    using type = vector<typename vec_impl<T,d-1>::type>;
    template <class... U> static type make_v(size_t n, U&&... x) { return type(n, vec_impl<T,d-1>::make_v(forward<U>(x)...)); }
};
template <class T> struct vec_impl<T,0> { using type = T; static type make_v(T const& x = {}) { return x; } };
template <class T, size_t d = 1> using vec = typename vec_impl<T,d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args&&... args) { return vec_impl<T,d>::make_v(forward<Args>(args)...); }
template <class T> void quit(T const& x) { cout << x << endl; exit(0); }
template <class T> constexpr bool chmin(T& x, T const& y) { if (x > y) { x = y; return true; } return false; }
template <class T> constexpr bool chmax(T& x, T const& y) { if (x < y) { x = y; return true; } return false; }
template <class It> constexpr auto sumof(It b, It e) { return accumulate(b,e,typename iterator_traits<It>::value_type{}); }
template <class T> int sz(T const& x) { return x.size(); }
template <class C, class T> int lbd(C const& v, T const& x) {
    return lower_bound(v.begin(), v.end(), x)-v.begin();
}
template <class C, class T> int ubd(C const& v, T const& x) {
    return upper_bound(v.begin(), v.end(), x)-v.begin();
}
// <<<
// >>> modint
template <uint32_t MOD>
struct modint {
    using u32 = uint32_t;
    using u64 = uint64_t;
    using i64 = int64_t;
    using M = modint;

    static constexpr u32 mul_inv(u32 n, int e = 5, u32 x = 1) {
        return e == 0 ? x : mul_inv(n, e-1, x*(2-x*n));
    }
    static constexpr u32 mod = MOD;
    static constexpr u32 nn = mul_inv(MOD);
    static constexpr u32 r2 = -u64(MOD) % MOD;

    u32 x;
    constexpr modint(i64 x = 0) : x(reduce(((x%=MOD)<0 ? x+MOD : x)*r2)) {}
    static constexpr u32 reduce(u64 w) {
        return u32(w >> 32) + MOD - i64((u64(u32(w) * nn) * MOD) >> 32);
    }
    constexpr i64 val() const {
        i64 r = reduce(x);
        if (r >= MOD) r -= MOD;
        return r;
    }
    constexpr operator i64() const { return val(); }
    constexpr bool operator==(M p) const { return val() == p.val(); }
    constexpr bool operator!=(M p) const { return val() != p.val(); }
    constexpr M operator+() const { return *this; }
    constexpr M operator-() const { M r; r.x = x ? i64(2*MOD)-x : 0; return r; }
    constexpr M &operator+=(M p) {
        i64 t = x; if (((t += p.x) -= 2*MOD) < 0) t += 2*MOD;
        x = t;
        return *this;
    }
    constexpr M &operator-=(M p) { return *this += -p; }
    constexpr M &operator*=(M p) { x = reduce(u64(x)*p.x); return *this; }
    constexpr M &operator/=(M p) { *this *= p.inv(); return *this; }

    constexpr M operator+(M p) const { return M(*this) += p; }
    constexpr M operator-(M p) const { return M(*this) -= p; }
    constexpr M operator*(M p) const { return M(*this) *= p; }
    constexpr M operator/(M p) const { return M(*this) /= p; }
    friend constexpr M operator+(i64 x, M y) { return M(x)+y; }
    friend constexpr M operator-(i64 x, M y) { return M(x)-y; }
    friend constexpr M operator*(i64 x, M y) { return M(x)*y; }
    friend constexpr M operator/(i64 x, M y) { return M(x)/y; }

    constexpr M inv() const { return pow(MOD - 2); }
    constexpr M pow(i64 n) const {
        if (n < 0) return inv().pow(-n);
        M v = *this, r = 1;
        for (; n > 0; n >>= 1, v *= v) if (n&1) r *= v;
        return r;
    }

    friend ostream &operator<<(ostream &os, M p) {
        return os << p.val();
    }
    friend istream &operator>>(istream &is, M &a) {
        u32 t; is >> t; a = t; return is;
    }
#ifdef LOCAL
    friend string to_s(M p) { return to_s(p.val(), MOD); }
#endif
};
// <<<
//constexpr int64_t MOD = 998244353;
constexpr int64_t MOD = 1e9+7;
using mint = modint<MOD>;
// >>> mod table
template <int32_t mod>
struct ModTable {
    static constexpr int32_t Size = 1e6 + 10;
    static_assert(Size <= mod, "");
    using ll = int64_t;
    int32_t fact[Size], finv[Size], inv[Size];
    ModTable() {
        fact[0] = fact[1] = finv[0] = finv[1] = inv[1] = 1;
        for (int i = 2; i < Size; i++) {
            fact[i] = ll(fact[i-1])*i % mod;
            inv[i] = mod - ll(inv[mod%i])*(mod/i) % mod;
            finv[i] = ll(finv[i-1])*inv[i] % mod;
        }
    }
};
const ModTable<MOD> mod_tab;

modint<MOD> fact(int n) {
    assert(0 <= n); assert(n < ModTable<MOD>::Size);
    return mod_tab.fact[n];
}
modint<MOD> finv(int n) {
    assert(0 <= n); assert(n < ModTable<MOD>::Size);
    return mod_tab.finv[n];
}
modint<MOD> C(int n, int k) {
    if (n < 0 || k < 0 || n < k) return 0;
    return fact(n)*finv(k)*finv(n-k);
}
modint<MOD> P(int n, int k) {
    assert(k >= 0);
    return fact(n)*finv(n-k);
}
// <<<

int32_t main() {
    int h,w,a,b; cin >> h >> w >> a >> b;

    mint sum = 0;
    rep (i,h-a) sum += C(h-a+b-1,i) * C(w-1+a-b,h-1-i);

    cout << sum << endl;
}


Measured memory_bytes: 12032