//  Copyright 2020 Nikita Golikov

#include <bits/stdc++.h>

using namespace std;

using i64 = int64_t;
using ui64 = uint64_t;

#ifdef GOLIKOV
mt19937_64 rng(566);
#else
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
#endif

template <typename T>
T rnd_helper(T from, T to, true_type) {
  return uniform_int_distribution<T>(from, to)(rng);
}

template <typename T>
T rnd_helper(T from, T to, false_type) {
  return uniform_real_distribution<T>(from, to)(rng);
}

template <typename T>
T rnd(T from, T to) {
  return rnd_helper(from, to, is_integral<T>{});
}

template <typename A, typename B, typename Cmp>
bool set_min(A &x, B const &y, Cmp &&cmp) {
  if (cmp(y, x)) {
    x = y;
    return true;
  }
  return false;
}

template <typename A, typename B>
bool set_min(A &x, B const &y) {
  return set_min(x, y, less<typename common_type<A, B>::type>{});
}

template <typename A, typename B>
bool set_max(A &x, B const &y) {
  return set_min(x, y, greater<typename common_type<A, B>::type>{});
}

#include <ext/pb_ds/assoc_container.hpp>

using namespace __gnu_pbds;

template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,
                         tree_order_statistics_node_update>;

template <typename K, typename V>
using ordered_map = tree<K, V, less<K>, rb_tree_tag,
                         tree_order_statistics_node_update>;

//  https://codeforces.com/blog/entry/62393
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    // http://xorshift.di.unimi.it/splitmix64.c
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }

  size_t operator()(uint64_t x) const {
    static const uint64_t
        FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
    return static_cast<size_t>(splitmix64(x + FIXED_RANDOM));
  }
};

#ifdef __cpp_deduction_guides
template <typename F>
struct rec_fun {
  F fun;

  rec_fun(F&& fun_) : fun(std::forward<F>(fun_)) {}

  template <typename... Args>
  decltype(auto) operator()(Args&&... args) const {
    return fun(*this, std::forward<Args>(args)...);
  }
};
#endif

#ifdef __cpp_inline_variables
template <typename T>
inline constexpr auto type_min = numeric_limits<T>::min();

template <typename T>
inline constexpr auto type_max = numeric_limits<T>::max();
#endif

//  fast alloc
#if 0
int const MAX_MEM = 1e8;
int mpos = 0;
char mem[MAX_MEM];
void* operator new(size_t n) {
  mpos += n;
  return (void*)(mem + mpos - n);
}
void operator delete (void*) noexcept {}
#endif

//  pragmas
#if 0
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4")
#pragma GCC optimize("unroll-loops")
#endif

int main() {
#ifdef GOLIKOV
  assert(freopen("in", "rt", stdin));
  auto _clock_start = chrono::high_resolution_clock::now();
#endif
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int h, w, a, b;
  cin >> h >> w >> a >> b;
  int const MOD = (int) 1e9 + 7;

  auto mul = [](i64 x, int y) {
    return (int) (x * y % MOD);
  };
  auto add_self = [](int& x, int y) {
    x += y;
    if (x >= MOD) {
      x -= MOD;
    }
  };
  auto pw = [&](int n, i64 deg) {
    int r = 1;
    while (deg) {
      if (deg & 1) {
        r = mul(r, n);
      }
      n = mul(n, n);
      deg >>= 1;
    }
    return r;
  };
  auto inv = [&](int n) {
    return pw(n, MOD - 2);
  };

  int const N = 2 * max(h, w) + 2;
  vector<int> fact(N + 1), rfact(N + 1);
  fact[0] = 1;
  for (int i = 1; i <= N; ++i) {
    fact[i] = mul(i, fact[i - 1]);
  }
  rfact[N] = inv(fact[N]);
  for (int i = N - 1; i >= 0; --i) {
    rfact[i] = mul(rfact[i + 1], i + 1);
  }

  auto choose = [&](int n, int k) {
    return mul(fact[n], mul(rfact[k], rfact[n - k]));
  };
  auto ways = [&](int r1, int c1, int r2, int c2) {
    int dr = r2 - r1;
    int dc = c2 - c1;
    return choose(dr + dc, dr);
  };
  int ans = 0;
  for (int r = 0; r < h - a; ++r) {
    add_self(ans, mul(ways(0, 0, r, b - 1), ways(r, b, h - 1, w - 1)));
  }
  cout << ans << '\n';

#ifdef GOLIKOV
  cerr << "Executed in " << chrono::duration_cast<chrono::milliseconds>(
      chrono::high_resolution_clock::now()
          - _clock_start).count() << "ms." << endl;
#endif
  return 0;
}


Measured memory_bytes: 1792