#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
#include <random>
#include <iomanip>
#include <unordered_set>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpii;
typedef vector<pair<ll,ll> > vpll;
typedef vector<vector<int> > vvi;
typedef vector<vector<char> > vvc;
typedef vector<vector<string> > vvs;
typedef vector<vector<ll> > vvll;
typedef map<int, int> mii;
typedef set<int> si;
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define arep(i,v) for(auto i : v)
#define irep(it, stl) for(auto it = stl.begin(); it != stl.end(); it++)
#define drep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define STLL(s) strtoll(s.c_str(), NULL, 10)
#define mp(p,q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int
// #define endl '\n';
#define fi first
#define se second
#define NONVOID [[nodiscard]]
constexpr int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
constexpr int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;} return 0;}
template <class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;} return 0;}
template <class T> inline void dump(T &v){irep(i, v){cout<<*i<<((i==--v.end())?'\n':' ');}}
inline string getline(){string s; getline(cin,s); return s;}
inline void yn(const bool b){b?fin("yes"):fin("no");}
inline void Yn(const bool b){b?fin("Yes"):fin("No");}
inline void YN(const bool b){b?fin("YES"):fin("NO");}
struct io{io(){ios::sync_with_stdio(false);cin.tie(0);}};
const int INF = INT_MAX;
constexpr ll LLINF = 1LL<<60;
constexpr ll MOD = 1000000007;
constexpr double EPS = 1e-9;






struct mint {
    ll x;
    mint(ll _x = 0):x((_x % MOD + MOD) % MOD) {}

    /* 初期化子 */
    mint operator+() const {
      return mint(x);
    }
    mint operator-() const {
      return mint(-x);
    }

    /* 代入演算子 */
    mint& operator+=(const mint a) {
        if ((x += a.x) >= MOD) x -= MOD;
        return *this;
    }
    mint& operator-=(const mint a) {
        if ((x += MOD - a.x) >= MOD) x -= MOD;
        return *this;
    }
    mint& operator*=(const mint a) {
        (x *= a.x) %= MOD;
        return *this;
    }
    mint& operator/=(const mint a) {
        x *= modinv(a).x;
        return (*this);
    }
    mint& operator%=(const mint a) {
        x %= a.x;
        return (*this);
    }
    mint& operator++() {
        ++x;
        if(x >= MOD) x -= MOD;
        return *this;
    }
    mint& operator--() {
        --x;
        if(x <0) x += MOD;
        return *this;
    }
    mint& operator&=(const mint a) {
        x &= a.x;
        return (*this);
    }
    mint& operator|=(const mint a) {
        x |= a.x;
        return (*this);
    }
    mint& operator^=(const mint a) {
        x ^= a.x;
        return (*this);
    }
    mint& operator<<=(const mint a) {
        x *= pow(2, a).x;
        return (*this);
    }
    mint& operator>>=(const mint a) {
        x /= pow(2, a).x;
        return (*this);
    }

    /* 算術演算子 */
    mint operator+(const mint a) const {
        mint res(*this);
        return res+=a;
    }
    mint operator-(const mint a) const {
        mint res(*this);
        return res-=a;
    }
    mint operator*(const mint a) const {
        mint res(*this);
        return res*=a;
    }
    mint operator/(const mint a) const {
        mint res(*this);
        return res/=a;
    }
    mint operator%(const mint a) const {
        mint res(*this);
        return res%=a;
    }
    mint operator&(const mint a) const {
        mint res(*this);
        return res&=a;
    }
    mint operator|(const mint a) const {
        mint res(*this);
        return res|=a;
    }
    mint operator^(const mint a) const {
        mint res(*this);
        return res^=a;
    }
    mint operator<<(const mint a) const {
        mint res(*this);
        return res<<=a;
    }
    mint operator>>(const mint a) const {
        mint res(*this);
        return res>>=a;
    }

    /* 条件演算子 */
    bool operator==(const mint a) const noexcept {
        return x == a.x;
    }
    bool operator!=(const mint a) const noexcept {
        return x != a.x;
    }
    bool operator<(const mint a) const noexcept {
        return x < a.x;
    }
    bool operator>(const mint a) const noexcept {
        return x > a.x;
    }
    bool operator<=(const mint a) const noexcept {
        return x <= a.x;
    }
    bool operator>=(const mint a) const noexcept {
        return x >= a.x;
    }

    /* ストリーム挿入演算子 */
    friend istream& operator>>(istream& is, mint& m) {
        is >> m.x;
        m.x = (m.x % MOD + MOD) % MOD;
        return is;
    }
    friend ostream& operator<<(ostream& os, const mint& m) {
        os << m.x;
        return os;
    }

    /* その他の関数 */
    mint modinv(mint a) {
        return pow(a, MOD - 2);
    }
    mint pow(mint x, mint n){
        mint res = 1;
        while(n.x > 0){
            if((n%2).x) res *= x;
            x *= x;
            n.x /= 2;
        }
        return res;
    }
};

// void verify(mint a, mint2 b){
//     if(a.x == b.x){
//         fin("\n== OK ==");
//     } else {
//         fin("!!!!!! NG !!!!!!");
//     }
// }


#define MAX_NCK 201010
mint f[MAX_NCK], rf[MAX_NCK];

bool isinit = false;

void init() {
    f[0] = 1;
    rf[0] = 1;
    for(int i = 1; i < MAX_NCK; i++) {
        f[i] = f[i - 1] * i;
        // rf[i] = modinv(f[i].x);
        rf[i] = f[i].pow(f[i], MOD - 2);
    }
}

mint nCk(mint n, mint k) {
    if(n < k) return 0;
    if(!isinit) {
        init();
        isinit = 1;
    }
    mint nl = f[n.x]; // n!
    mint nkl = rf[n.x - k.x]; // (n-k)!
    mint kl = rf[k.x]; // k!
    mint nkk = (nkl.x * kl.x);

    return nl * nkk;
}

mint calc(mint x1, mint y1, mint x2, mint y2){
    mint tate=y2-y1;
    mint yoko=x2-x1;
    return nCk(tate+yoko,min(yoko,tate));
}

int main() {

    mint h, w, a, b;
    cin >> h >> w >> a >> b;
    vector<pair<mint, mint>> v;
    mint y = h - a - 1;
    mint x = b;
    while(y >= 0 && x < w) {
        v.pb(mp(x, y));
        ++x;
        --y;
    }
    mint ans = 0;
    rep(i, v.size()) {
        ans+=calc(0, 0, v[i].first, v[i].second)\
            *calc(v[i].first, v[i].second, w - 1, h - 1);
    }
    fin(ans);
}



Measured memory_bytes: 5620