#include<iostream>
#include<fstream>
#include<bitset>
#include<string>
#include<vector>
#include<algorithm>
#include<cmath>
#include<map>
#include<set>
#include<iomanip>
#include<queue>
#include<stack>
#include<numeric>
#include<utility>
#include<regex>
#include<climits>

void Init() {
	std::cin.tie(0); std::ios::sync_with_stdio(false);
	struct Init_caller { Init_caller() { Init(); } }caller;
}


#define int LL
#define rep(i,n) for(LL (i)=0;(i)<(n);(i)++)
#define all(a) (a).begin(),(a).end()
#define size(s) ((LL)s.size())
#define F first
#define S second
#define check() cout<<"! ! !"
#define endl "\n"
#define _y() cout<<"Yes"<<endl
#define _Y() cout<<"YES"<<endl
#define _n() cout<<"No"<<endl
#define _N() cout<<"NO"<<endl
#define INT_INF INT_MAX
#define INF LLONG_MAX
#define MOD ((int)pow(10,9)+7)



using namespace std;

using LL = long long;
using st = string;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vd = vector<double>;
using vvd = vector<vd>;
using vvvd = vector<vvd>;
using vc = vector<char>;
using vvc = vector<vc>;
using vs = vector<st>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
using qi = queue<int>;
using qc = queue<char>;
using qs = queue<st>;
using si = stack<int>;
using sc = stack<char>;
using ss = stack<st>;
using pi = pair<int, int>;
using ppi = pair<pi, int>;
using mii = map<int, int>;
using mpii = map<pi, int>;
using mib = map<int, bool>;
using mci = map<char, int>;
using msb = map<st, bool>;
using vpi = vector<pi>;
using vppi = vector<ppi>;
using spi = stack<pi>;
using qpi = queue<pi>;



//4,2,8,6,1,7,3,9
int dx[] = { -1,0,0,1,-1,-1,1,1 };
int dy[] = { 0,1,-1,0,1,-1,1,-1 };


void y_n(bool p) {
	p ? _y() : _n();
}

void Y_N(bool p) {
	p ? _Y() : _N();
}

LL vmax(vi v) {
	int n = size(v);
	int MAX = 0;
	rep(i, n) {
		MAX = max(MAX, v[i]);
	}
	return MAX;
}

LL vmin(vi v) {
	int n = size(v);
	int MIN = INF;
	rep(i, n) {
		MIN = min(MIN, v[i]);
	}
	return MIN;
}

LL vsum(vi v) {
	int n = size(v);
	int sum = 0;
	rep(i, n) {
		sum += v[i];
	}
	return sum;
}

LL gcd(LL a, LL b) {
	if (b == 0) {
		swap(a, b);
	}
	LL r;
	while ((r = a % b) != 0) {
		a = b;
		b = r;
	}
	return b;
}
LL lcm(LL a, LL b) {
	return (a / gcd(a, b) * b);
}

bool is_square(int n) {
	if ((int)sqrt(n)*(int)sqrt(n) == n) {
		return true;
	}
	else {
		return false;
	}
}


bool is_prime(int n) {
	if (n == 1) {
		return false;
	}
	else {
		for (int i = 2; i*i <= n; i++) {
			if (n % i == 0) {
				return false;
			}
		}
	}
	return true;
}

void dec_num(int n, vi &v) {
	int a = 2;
	v.push_back(1);
	v.push_back(n);
	while (a*a <= n) {
		if (n%a == 0) {
			v.push_back(a);
			v.push_back(n / a);

		}
		a++;
	}
	sort(all(v));
}


void dec_prime(int n, vi &v) {
	int a = 2;
	while (a*a <= n) {
		if (n % a == 0) {
			v.push_back(a);
			n /= a;
		}
		else {
			a++;
		}
	}
	v.push_back(n);
}


int sieve_prime(LL a, LL b) {
	if (a > b)swap(a, b);
	vb s(b + 1, true);
	int cnt_a = 0, cnt_b = 0;
	for (int i = 2; i <= b; i++) {
		for (int j = 2; i*j <= b; j++) {
			s[i*j] = false;
		}
	}
	for (int i = 2; i <= b; i++) {
		if (s[i]) {
			//cout << i << " ";
			if (i < a) {
				cnt_a++;
			}
			cnt_b++;
		}
	}
	return cnt_b - cnt_a;
}


LL factorial(LL n) {
	LL a = 1, ret = 1;
	while (a < n) {
		a++;
		ret *= a;
		//ret %= MOD;
	}
	return ret;
}


const int COMBMAX = 4000;
int comb[COMBMAX+5][COMBMAX+5];

void init_comb() {
	comb[0][0] = 1;
	rep(i, COMBMAX) {
		rep(j, i + 1) {
			comb[i + 1][j] += comb[i][j];
			comb[i + 1][j] %= MOD;
			comb[i + 1][j + 1] += comb[i][j];
			comb[i + 1][j + 1] %= MOD;
		}
	}
}

int combination(int n, int k) {
	if (k<0 || k>n)return 0;
	else return comb[n][k];
}


const int COMBMODMAX = 510000;
int fac[COMBMODMAX], facinv[COMBMODMAX], inv[COMBMODMAX];

void init_comb_mod() {
	fac[0] = fac[1] = 1;
	facinv[0] = facinv[1] = 1;
	inv[1] = 1;
	for (int i = 2; i < COMBMODMAX; i++) {
		fac[i] = fac[i - 1] * i%MOD;
		inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
		facinv[i] = facinv[i - 1] * inv[i] % MOD;
	}
}

int comb_mod(int n, int k) {
	if (n < k)return 0;
	if (n < 0 || k < 0)return 0;
	return fac[n] * (facinv[k] * facinv[n - k] % MOD) % MOD;
}

int pow_mod(int x, int n, int p) {
	if (n == 0)return 0;
	int res = pow_mod(x*x%p, n / 2, p);
	if (n % 2 == 1)res = res * x % p;
	return res;
}



vi par;

int root(int x) {
	if (par[x] == x) {
		return x;
	}
	else {
		return par[x] = root(par[x]);
	}
}

void unite(int x, int y) {
	if (root(x) == root(y)) {
		return;
	}
	else {
		par[root(x)] = root(y);
		return;
	}
}

bool same(int x, int y) {
	return root(x) == root(y);
}

struct edge {
	int to;
	int cost;
};


using ve = vector<edge>;
using vve = vector<ve>;

/*****************************************************************************/
signed main() {

	int h, w, a, b;
	cin >> h >> w >> a >> b;
	init_comb_mod();
	int ans = 0;
	rep(i, w - b) {
		ans += comb_mod(h - a - 1 + b, h - a - 1 - i)*comb_mod(a + w - b - 1, a + i) % MOD;
	}
	cout << ans % MOD;
	return 0;
}

Measured memory_bytes: 12544