#line 1 "main.cpp"
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cstdint>
#include <cstdlib>
#include <cmath>
#include <complex>
#include <chrono>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <vector>
#include <random>
#include <utility>
#include <limits>
#include <list>
#include <type_traits>

/* template start */
 
#define rep(i, a, b) for (long long i = (a); (i) < (b); (i)++)
#define all(i) i.begin(), i.end()

#ifdef LOCAL
#define debug(...) std::cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

void debug_out(){std::cerr<<std::endl;}

template<typename Head,typename... Tail>
void debug_out(Head h,Tail... t){
  std::cerr<<" "<<h;
  if(sizeof...(t)>0)std::cout<<" :";
  debug_out(t...);
}
 
template <typename T1, typename T2>
std::ostream& operator<<(std::ostream& os, std::pair<T1, T2> pa) {
  return os << pa.first << " " << pa.second;
}
 
template <typename T>
std::ostream& operator<<(std::ostream& os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}
 
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);}

template<typename Num>
constexpr Num mypow(Num a, long long b) {
  if(b==0)return 1;
  if (a==0)return 0;
  Num x = 1;
  while (b > 0) {
    if(b & 1)x*=a;
    a*=a;
    b >>= 1;
  }
  return x;
}

/* template end */

using ll = long long;

#line 2 "/mnt/c/Users/Imperi/Documents/cp-library/lib/math/FactorialTable.hpp"

#line 2 "/mnt/c/Users/Imperi/Documents/cp-library/lib/utility/modint.hpp"

/*
  author:noshi91
  reference:https://noshi91.hatenablog.com/entry/2019/03/31/174006
            https://github.com/noshi91/Library/blob/master/other/modint.cpp

  1つめのmodintにoperator==,!=を追加したものです

  thx @noshi91!!
*/

#line 14 "/mnt/c/Users/Imperi/Documents/cp-library/lib/utility/modint.hpp"

template <std::uint_fast64_t Modulus> class modint {
  using u64 = std::uint_fast64_t;

public:
  u64 a;

  constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {}
  constexpr u64 &value() noexcept { return a; }
  constexpr const u64 &value() const noexcept { return a; }
  constexpr bool operator==(const modint rhs) const noexcept {return a==rhs.a;}
  constexpr bool operator!=(const modint rhs) const noexcept {return !(*this==rhs);}
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    a += rhs.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (a < rhs.a) {
      a += Modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    a = a * rhs.a % Modulus;
    return *this;
  }
  constexpr modint &operator/=(modint rhs) noexcept {
    u64 exp = Modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }
};
#line 4 "/mnt/c/Users/Imperi/Documents/cp-library/lib/math/FactorialTable.hpp"

#line 8 "/mnt/c/Users/Imperi/Documents/cp-library/lib/math/FactorialTable.hpp"

template<std::size_t N,std::uint_fast64_t MOD>
class Factorial{
  public:
  using mint=modint<MOD>;
  using size_t=std::size_t;
  private:
  std::vector<mint> factorial,factorial_inv;
  public:
  Factorial():factorial(N+1),factorial_inv(N+1){
    factorial[0]=1;
    for(size_t i=1;i<N+1;i++)factorial[i]=factorial[i-1]*i;
    factorial_inv[N]=mint(1)/factorial[N];
    for(size_t i=N;i>0;i--)factorial_inv[i-1]=factorial_inv[i]*i;
  }

  mint fact(size_t pos)const{
    assert(0<=pos&&pos<=N);
    return factorial[pos];
  }
  mint fact_inv(size_t pos)const{
    assert(0<=pos&&pos<=N);
    return factorial_inv[pos];
  }
  mint binom(size_t n,size_t k)const{
    assert(0<=n&&n<=N);
    assert(0<=k&&k<=n);
    return fact(n)*fact_inv(k)*fact_inv(n-k);
  }
};
#line 85 "main.cpp"

constexpr ll MOD=1e9+7;
using mint=modint<MOD>;

int main() {
  std::cin.tie(nullptr);
  std::ios::sync_with_stdio(false);

  ll h,w,a,b;
  std::cin>>h>>w>>a>>b;

  Factorial<200010,MOD> table;

  mint ans=0;

  rep(i,0,w-b){
    ans+=table.binom(w-1-i+h-a-1,h-a-1)*table.binom(a-1+i,a-1);
  }

  std::cout<<ans.value()<<"\n";

  return 0;
}


Measured memory_bytes: 6320