import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.15f";

static string[] s_rd;
T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
string RDR()() { return readln.chomp; }
T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; }
T[] RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[][] RDA2(T = long)(size_t n, T[] fix = []) { auto r = new T[][](n); foreach (i; 0..n) { r[i] = readln.chomp.split.to!(T[]); foreach (j, e; fix) r[i][j] += e; } return r; }
size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
long lcm(long x, long y) { return x * y / gcd(x, y); }

long mod = 10^^9 + 7;
//long mod = 998244353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }

struct Cmb
{
	void init(long n)
	{
		long powmod(long a, long p)
		{
			long ans = 1;
			long mul = a;
			while (p > 0)
			{
				if ((p & 1) == 1)
					modm(ans, mul);
				p >>= 1;
				modm(mul, mul);
			}
			return ans;
		}

		++n;
		fact = new long[2][](n);
		fact[0][0] = 1;
		foreach (i; 1..n)
		{
			fact[i][0] = fact[i-1][0];
			modm(fact[i][0], i);
		}
		fact[n-1][1] = powmod(fact[n-1][0], mod - 2);
		foreach_reverse (i; 0..n-1)
		{
			fact[i][1] = fact[i+1][1];
			modm(fact[i][1], i+1);
		}
	}

	long get(long a, long b)
	{
		long r = fact[a][0];
		modm(r, fact[b][1]);
		modm(r, fact[a-b][1]);
		return r;
	}

	long[2][] fact;
}

void main()
{
	auto H = RD;
	auto W = RD;
	auto A = RD;
	auto B = RD;

	Cmb cmb;
	cmb.init(H+W);

	long ans;
	foreach (x; 0..W-B)
	{
		auto c1 = cmb.get(B+x+H-A-1, B+x);
		auto c2 = cmb.get(W-B-x-1+A-1, A-1);
		c1.modm(c2);
		ans.moda(c1);
	}

	writeln(ans);
	stdout.flush();
	debug readln();
}