#define DEBUG 0
#include <bits/stdc++.h>
#define all(v) (v).begin(), (v).end()
#define pb push_back
#define REP(i,n) for(int i=0; i<(n); i++)
#define REP2(i,x,n) for(int i=x; i<(n); i++)
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
template<class T>using numr=std::numeric_limits<T>;
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; }
const int INF = 1e9;
const ll LLINF = 1e16;
const int mod = 1000000007;
const int MOD2 = 998244353;
void debug_impl() { std::cerr << std::endl; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) { std::cerr << " " << head; debug_impl(tail...); }
#if DEBUG
#define debug(...)\
    do {\
        std::cerr << std::boolalpha << "[" << #__VA_ARGS__ << "]:";\
        debug_impl(__VA_ARGS__);\
        std::cerr << std::noboolalpha;\
    } while (false)
#else
#define debug(...) {}
#endif

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr>
std::istream& operator>> (std::istream& is, Container& v)
    { for (auto & x : v) { is >> x; } return is; }

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr >
std::ostream& operator<< (std::ostream& os, Container const& v) {
os << "{";
    for (auto it = v.begin(); it != v.end(); it++)
        {os << (it != v.begin() ? "," : "") << *it;}
    return os << "}";
}
template< int mod >
struct ModInt {
  int x;

  ModInt() : x(0) {}

  ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

  ModInt &operator+=(const ModInt &p) {
    if((x += p.x) >= mod) x -= mod;
    return *this;
  }

  ModInt &operator-=(const ModInt &p) {
    if((x += mod - p.x) >= mod) x -= mod;
    return *this;
  }

  ModInt &operator*=(const ModInt &p) {
    x = (int) (1LL * x * p.x % mod);
    return *this;
  }

  ModInt &operator/=(const ModInt &p) {
    *this *= p.inverse();
    return *this;
  }

  ModInt operator-() const { return ModInt(-x); }

  ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }

  ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }

  ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }

  ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

  bool operator==(const ModInt &p) const { return x == p.x; }

  bool operator!=(const ModInt &p) const { return x != p.x; }

  ModInt inverse() const {
    int a = x, b = mod, u = 1, v = 0, t;
    while(b > 0) {
      t = a / b;
      swap(a -= t * b, b);
      swap(u -= t * v, v);
    }
    return ModInt(u);
  }

  ModInt pow(int64_t n) const {
    ModInt ret(1), mul(x);
    while(n > 0) {
      if(n & 1) ret *= mul;
      mul *= mul;
      n >>= 1;
    }
    return ret;
  }

  friend ostream &operator<<(ostream &os, const ModInt &p) {
    return os << p.x;
  }

  friend istream &operator>>(istream &is, ModInt &a) {
    int64_t t;
    is >> t;
    a = ModInt< mod >(t);
    return (is);
  }

  static int get_mod() { return mod; }
};

using modint = ModInt< mod >;

modint fact[200010];
 
modint nCr(int n, int r){
    return fact[n]/(fact[n-r]*fact[r]);
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    int H, W, A, B;
    cin >> H >> W >> A >> B;
    fact[0] = 1;
    for(ll i=1; i<=200000; i++){
        fact[i] = (fact[i-1] * i);
    }
 
    modint ans = 0;
    for(int i=B; i<W; i++){
        modint tmp = nCr((H-A-1)+i, H-A-1) * nCr((A-1)+(W-i-1), A-1);
        ans += tmp;
    }
    cout << ans << endl;
}


Measured memory_bytes: 4420