#include "bits/stdc++.h"
using namespace std;

//#define int long long
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(a) (a).begin(),(a).end()
#define dump(o) if(DEBUG){cerr<<#o<<" "<<o<<endl;}
#define dumpc(o) if(DEBUG){cerr<<#o; for(auto &e:(o))cerr<<" "<<e;cerr<<endl;}
using ll = long long; using ull = unsigned long long; using pii = pair<int, int>;
static const int INF = 0x3f3f3f3f; static const long long INFL = 0x3f3f3f3f3f3f3f3fLL;
static const int MOD = 1e9 + 7;
static const bool DEBUG = false;

template<int MOD>
struct ModInt {
	static const int Mod = MOD;
	unsigned x;
	ModInt() : x(0) {}
	ModInt(signed sig) { int sigt = sig % MOD; if (sigt < 0) sigt += MOD; x = sigt; }
	ModInt(signed long long sig) { int sigt = sig % MOD; if (sigt < 0) sigt += MOD; x = sigt; }
	int get() const { return (int)x; }

	ModInt &operator+=(ModInt that) { if ((x += that.x) >= MOD) x -= MOD; return *this; }
	ModInt &operator-=(ModInt that) { if ((x += MOD - that.x) >= MOD) x -= MOD; return *this; }
	ModInt &operator*=(ModInt that) { x = (unsigned long long)x * that.x % MOD; return *this; }
	ModInt &operator/=(ModInt that) { return *this *= that.inverse(); }

	ModInt operator+(ModInt that) const { return ModInt(*this) += that; }
	ModInt operator-(ModInt that) const { return ModInt(*this) -= that; }
	ModInt operator*(ModInt that) const { return ModInt(*this) *= that; }
	ModInt operator/(ModInt that) const { return ModInt(*this) /= that; }

	ModInt inverse() const {
		signed a = x, b = MOD, u = 1, v = 0;
		while (b) {
			signed t = a / b;
			a -= t * b; std::swap(a, b);
			u -= t * v; std::swap(u, v);
		}
		if (u < 0) u += Mod;
		ModInt res; res.x = (unsigned)u;
		return res;
	}
};
template <int M>
ostream &operator << (ostream &os, const ModInt<M> &m) { return os << m.x; }
template <int M>
istream &operator >> (istream &is, ModInt<M> &m) { signed long long s; is >> s; m = ModInt<M>(s); return is; };

typedef ModInt<1000000007> mint;

//nCrで用いる
vector<mint> fact, factinv;
//nCrで用いる 予め計算しておく
void nCr_computeFactinv(int N) {
	N = min(N, mint::Mod - 1);
	fact.resize(N + 1); factinv.resize(N + 1);
	fact[0] = 1;
	rep(i, 1, N + 1) fact[i] = fact[i - 1] * i;
	factinv[N] = fact[N].inverse();
	for (int i = N; i >= 1; i--) factinv[i - 1] = factinv[i] * i;
}
mint nCr(int n, int r) {
	if (n >= mint::Mod)
		return nCr(n % mint::Mod, r % mint::Mod) * nCr(n / mint::Mod, r / mint::Mod);
	return r > n ? 0 : fact[n] * factinv[n - r] * factinv[r];
}

int main() {
	for (int H, W, A, B; cin >> H >> W >> A >> B;) {
		nCr_computeFactinv(H + W);
		mint ans;
		mint ans2;
		if(DEBUG)rep(i, 0, H - A) {
			ans += nCr((B - 1) + i, i) * nCr((W - 1 - B) + (H - 1 - i), H - 1 - i);
			if (DEBUG)cerr << "ans += nCr(" << (B - 1) + i << "," << i << ")*nCr(" << (W - 1 - B) + (H - 1 - i) << "," << H - 1 - i << ")" << endl;
		}
		rep(i, 0, W - B) {
			ans2 += nCr(H - A - 1 + B + i, H - A - 1) * nCr(A - 1 + W - B - 1 - i, A - 1);
			if (DEBUG)cerr << "ans2 += nCr(" << H - A - 1 + B + i << "," << H - A - 1 << ")*nCr(" << A - 1 + W - B - 1 - i << "," << A - 1 << ")" << endl;
		}
		if (DEBUG)cerr << ans << endl;
		cout << ans2 << endl;
	}
	return 0;
}

Measured memory_bytes: 1920