#define _USE_MATH_DEFINES
#include <bits/stdc++.h>

using namespace std;

using i64 = long long;
#define forn(a, e) for (i64 a = 0; a < (i64)(e); a++)
#define forr(a, s, e) for (i64 a = s; a < (i64)(e); a++)
#define fore(e, a) for (auto& e : a)

#ifdef LOCAL
#define logv(a) {cerr << #a << " = "; fore(e, a) {cerr << e << " ";} cerr << "\n";}
#define logvp(a) {cerr << #a << " = "; fore(e, a) {cerr << "(" << e.first << ", " << e.second << ") ";} cerr << "\n";}
#define logvv(a) {cerr << #a << " = \n"; fore(r, a) { fore(e, r) {cerr << e << " ";} cerr << "\n";} }
#define logvf(a, field) {cerr << #a"."#field << " = \n"; fore(e, a) { cerr << e.field << " ";} cerr << "\n"; }
#define logvff(a, f1, f2) {cerr << #a".{"#f1 << ", "#f2 << "} = \n"; fore(e, a) { cerr << "(" << e.f1 <<", " << e.f2 << ") ";} cerr << "\n"; }
#define logs(a) cerr << #a << " = " << (a) << "\n";
#define logss(a, b) cerr << #a << " = " << (a) << ", " << #b << " = " << (b) << "\n";
#define logp(a) cerr << #a << " = " << "(" << a.first << ", " << a.second << ")" << "\n";
#define cond(pred, stmt) if (pred) { stmt }
#else
#define logv(a)
#define logvp(a)
#define logvv(a)
#define logvf(a, field)
#define logvff(a, f1, f2)
#define logs(a)
#define logss(a, b)
#define logp(a)
#define cond(pred, stmt)
#endif

using iip = pair<int, int>;
using llp = pair<i64, i64>;
using ivec = vector<int>;
using llvec = vector<i64>;
using svec = vector<string>;
template<typename T> using vec = vector<T>;

template<typename T, typename Dim>
auto make_vec(T value, Dim dim) { return vector<T>(dim, value); }
template<typename T, typename Dim1, typename... Dim>
auto make_vec(T value, Dim1 dim1, Dim... dims) { return make_vec(make_vec(value, dims...), dim1); }

template<typename T>
bool uax(T& v, const T& newv) { if (v < newv) { v = newv; return true; } else return false; }
template<typename T>
bool uin(T& v, const T& newv) { if (v > newv) { v = newv; return true; } else return false; }

template<typename T>
istream& operator>>(istream& is, vector<T>& c) { for (auto& e : c) is >> e; return is; }
template<typename T, size_t N>
istream& operator>>(istream& is, array<T, N>& c) { for (auto& e : c) is >> e; return is; }

template<typename ...T>
istream& read(T&... args) { return (cin >> ... >> args); }

static mt19937 rande(123123);
template<typename T>
T rand_int(T from, T to) { uniform_int_distribution<T> distr(from, to); return distr(rande); }

const i64 INF = 1e18;
const i64 M = 1e9 + 7;

i64 bpow(i64 a, i64 p) {
    if (p == 1) {
        return a;
    }
    if (p == 0) {
        return 1;
    }

    i64 res = bpow(a, p / 2);
    res *= res;
    res %= M;

    if (p % 2) {
        res *= a;
        res %= M;
    }

    return res;
}

i64 inv(i64 a) {
    return bpow(a, M - 2);
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    rande.seed(chrono::steady_clock::now().time_since_epoch().count());

    i64 h, w, a, b;
    while (read(h, w, a, b)) {
        llvec fact(h + w + 1);
        fact[0] = 1;
        forr(i, 1, fact.size()) {
            fact[i] = (i * fact[i - 1]) % M;
        }

        auto bc = [&](int n, int k) {
            return fact[n] * inv(fact[k] * fact[n - k] % M) % M;
        };

        i64 ans = 0;
        int n1 = b + h - a - 2;
        int k1 = b - 1;
        i64 c1 = bc(n1, k1);
        int n2 = a + w - b - 1;
        int k2 = w - b - 1;
        i64 c2 = bc(n2, k2);
        forn(i, h - a) {
            ans += c1 * c2 % M;
            ans %= M;
            c1 = (c1 * (n1 - k1) % M) * inv(n1) % M;
            n1--;
            n2++;
            c2 = (c2 * n2 % M) * inv(n2 - k2) % M;
        }
        cout << ans << endl;
    }
}

Measured memory_bytes: 4760