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

#define fs first
#define sc second
#define pb emplace_back
#define mp make_pair
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()

constexpr int mod = 1e9 + 7;
constexpr int32_t inf = 1001001001;
constexpr int64_t infll = 1001001001001001001ll;
constexpr int dx[] = {0, -1, 1, 0, -1, 1, -1, 1}, dy[] = {-1, 0, 0, 1, -1, -1, 1, 1};
const string YES = "YES", NO = "NO", Yes = "Yes", No = "No", yes = "yes", no = "no";

// clang-format off
// ostream &operator<<(ostream &os, __int128_t value) { if (ostream::sentry(os)) { __uint128_t tmp = value < 0 ? -value : value; char buffer[64]; char *d = end(buffer); do { --d; *d = "0123456789"[tmp % 10]; tmp /= 10; } while (tmp != 0); if (value < 0) { --d; *d = '-'; } int len = end(buffer) - d; if (os.rdbuf()->sputn(d, len) != len) { os.setstate(ios_base::badbit); }} return os; }
// istream &operator>>(istream &is, __int128_t &value) { string in; is >> in; value = 0; for (const char &c : in) { if ('0' <= c && c <= '9') value = 10 * value + (c - '0'); } if (in[0] == '-') value *= -1; return is; }
// ostream &operator<<(ostream &os, __uint128_t value) { if (ostream::sentry(os)) { char buffer[64]; char *d = end(buffer); do { --d; *d = "0123456789"[value % 10]; value /= 10; } while (value != 0); int len = end(buffer) - d; if (os.rdbuf()->sputn(d, len) != len) { os.setstate(ios_base::badbit); }} return os; }
// istream &operator>>(istream &is, __uint128_t &value) { string in; is >> in; value = 0; for (const char &c : in) { if ('0' <= c && c <= '9') value = 10 * value + (c - '0'); } return is; }
template <typename T> ostream &operator<<(ostream &os, vector<T> &v) { os << v[0]; for (int i = 1; i < v.size(); ++i) os << " " << v[i]; return os; }
template <typename T> istream &operator>>(istream &is, vector<T> &v) { for (T &in : v) is >> in; return is; }
template <typename T1, typename T2> ostream &operator<<(ostream &os, pair<T1, T2> p) { os << p.fs << " " << p.sc; return os; }
template <typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p) { is >> p.fs >> p.sc; return is; }

struct IoSetup { IoSetup(){ cin.tie(0); ios::sync_with_stdio(0); cout << fixed << setprecision(10); cerr << fixed << setprecision(10); } } iosetup;

inline int64_t in() { int64_t x = 0; cin >> x; return x; }

template <typename T> void sort(vector<T> &v) { sort(all(v)); }
template <typename T> vector<T> make_v(size_t a, T b) { return vector<T>(a, b); }
template <typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v(ts...))>(a, make_v(ts...)); }
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }
// clang-format on

struct ModCombination {
  ModCombination(unsigned int n) : n(n), F(n + 1, 1), I(n + 1, 1) {
    for (int i = 1; i <= n; ++i) F[i] = 1ll * i * F[i - 1] % mod;
    for (int64_t i = mod - 2, j = F[n]; i; i >>= 1) {
      if (i & 1) I[n] = I[n] * j % mod;
      j = j * j % mod;
    }
    for (int i = n - 1; i; --i) I[i] = I[i + 1] * (i + 1ll) % mod;
  }

  unsigned int n;
  vector<int> F, I;

  int operator()(int p, int k) {
    if (k < 0 || k > p) return 0;
    return 1ll * F[p] * I[k] % mod * I[p - k] % mod;
  }
};

signed main(int32_t argc, char *argv[]) {
  int H = in(), W = in(), A = in(), B = in();
  ModCombination mC(H + W);

  int ans = 0;
  for (int i = B + 1; i <= W; ++i) {
    (ans += (int64_t)mC(H - A + i - 2, i - 1) * mC(W - i + A - 1, A - 1) % mod) %= mod;
  }

  cout << ans << endl;
}


Measured memory_bytes: 1792