#include "bits/stdc++.h"
using namespace std;
#define Rep(i,n) for(int i=0;i<(int)(n);i++)
#define For(i,n1,n2) for(int i=(int)(n1);i<(int)(n2);i++)
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define RREP(i,n) for(ll i=((ll)(n)-1);i>=0;i--)
#define FOR(i,n1,n2) for(ll i=(ll)(n1);i<(ll)(n2);i++)
#define RFOR(i,n1,n2) for(ll i=((ll)(n1)-1);i>=(ll)(n2);i--)
#define all(a)  (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define oorret 0
#define oor(x) [&](){try{x;} catch(const out_of_range& oor){return oorret;} return x;}()
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
template<typename T1, typename T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return 1; }return 0; }
template<typename T1, typename T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return 1; }return 0; }
template<class Type>struct is_vector : std::false_type {};
template<class ValueType, class Alloc>struct is_vector<std::vector<ValueType, Alloc>> : std::true_type {};
template <typename T> inline ostream& operator << (ostream& out, const vector<T>& v) {
    if (v.empty())return out;
    constexpr bool is_vector_v = is_vector<T>::value;
    if (is_vector_v)for (auto itr = v.begin(); itr != v.end();)out << (*itr),out << ((++itr != v.end()) ? "\n" : "");
    else for (auto itr = v.begin(); itr != v.end();)out << (*itr),out << ((++itr != v.end()) ? " " : "");
    return out;
}
inline void put() {}
template<class T> inline void put(const T& first) { std::cout << first; printf("\n"); }
template<class T, class... N> inline void put(const T& first, const N& ... rest) { std::cout << first; printf(" "); put(rest...); }
inline void putn() {}
template<class T, class... N> inline void putn(const T& first, const N& ... rest) { std::cout << first; printf("\n"); putn(rest...); }

template<typename T, typename U>
inline T pow(T x, U exp) {
    if (exp <= 0) {
        return 1;
    }
    if (exp % 2 == 0) {
        T d = pow(x, exp / 2);
        return d * d;
    }
    else {
        return (x * pow(x, exp - 1));
    }
}

template<typename T>
inline T fact(T n, vector<T>& table) {
    if (n >= (int)table.size()) {
        uint_fast32_t s = table.size();
        for (T i = s; i < n + 1; ++i) {
            table.push_back(table.back() * i);
        }
    }
    if (n < 0) return 1;
    else return table[n.a];
}

template<typename T>
inline T comb(T n, T m, vector<T>& table) {//nCm
    if (n < m)return 0;
    if (n - m < m)return comb(n, n - m, table);
    else return fact(n, table) / fact(m, table) / fact(n - m, table);
}

class RuntimeModInt {
    using lint = int_fast64_t;
    static lint &mod() {static lint Mod = 0;return Mod;}
public:
    lint a;
    RuntimeModInt(lint val = 0){if(val >= get_mod()){val %= get_mod();}a=val;}
    static void set_mod(const lint x) { mod() = x; }
    static lint get_mod() { return mod(); }
    RuntimeModInt operator-() {return RuntimeModInt(get_mod() - a);}//単項-演算子(-a)のオーバーロード
    RuntimeModInt operator=(const RuntimeModInt& n) { a = n.a; return a; }
    RuntimeModInt operator+(const RuntimeModInt& n) { if ((a + n.a) >= get_mod()) { return a + n.a - get_mod(); } else { return a + n.a; } }
    RuntimeModInt operator-(const RuntimeModInt& n) {return a+(get_mod()-n.a);}
    RuntimeModInt operator*(const RuntimeModInt& n) { return a * n.a; }
    RuntimeModInt operator/(const RuntimeModInt& n) { return (*this) * pow(n, get_mod() - 2); }
    RuntimeModInt& operator+=(const RuntimeModInt& n) { (*this) = (*this) + n; return *this; }
    RuntimeModInt& operator-=(const RuntimeModInt& n) { (*this) = (*this) + (get_mod()-n.a); return *this; }
    RuntimeModInt& operator*=(const RuntimeModInt& n) { (*this) = (*this) * n; return *this; }
    RuntimeModInt& operator/=(const RuntimeModInt& n) { (*this) = (*this) / n; return *this; }
    RuntimeModInt& operator++(int) { (*this) = (*this) + 1; return *this; }//前置インクリメントs(++a)のオーバーロード
    RuntimeModInt& operator++() { (*this) = (*this) + 1; return *this; }//後置インクリメント(a++)のオーバーロード
    RuntimeModInt& operator--(int) { (*this) = (*this) + (get_mod()-1); return *this; }//前置デクリメント(--a)のオーバーロード
    RuntimeModInt& operator--() { (*this) = (*this) + (get_mod()-1); return *this; }//後置デクリメント(a--)のオーバーロード
    RuntimeModInt inv() { RuntimeModInt temp(1); return temp / (*this); }//逆数を返す関数 return (*this)/(*this)/(*this);でもいい
    bool operator<(const RuntimeModInt& n) { return a < n.a; }
    bool operator<=(const RuntimeModInt& n) { return a <= n.a; }
    bool operator>(const RuntimeModInt& n) { return a > n.a; }
    bool operator>=(const RuntimeModInt& n) { return a >= n.a; }
    bool operator==(const RuntimeModInt& n) { return a == n.a; }
    bool operator!=(const RuntimeModInt& n) { return a != n.a; }
    //下の関係演算子はpow関数で要請される
    bool operator<(const int& n) { return a < n; }
    bool operator<=(const int& n) { return a <= n; }
    bool operator>(const int& n) { return a > n; }
    bool operator>=(const int& n) { return a >= n; }
    bool operator==(const int& n) { return a == n; }
    RuntimeModInt operator%(const int& n) { return a % n; }
};
inline ostream& operator <<(ostream& o, const RuntimeModInt& t) {o << t.a;return o;}
inline istream& operator >>(istream& i, RuntimeModInt& t) {i >> t.a;return i;}

int main(){
    uint_fast64_t mod = 1e9+7;
    RuntimeModInt::set_mod(mod);
    RuntimeModInt h,w,a,b;
    cin >> h >> w >> a >> b;
    vector<RuntimeModInt> table(1,1);
    RuntimeModInt res;
    for(RuntimeModInt i=1;i<h-a+1;++i){
        res += comb(b+i-2,i-1,table)*comb(w-b+h-i-1,h-i,table);
    }
    put(res);
    return 0;
}


Measured memory_bytes: 2420