using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;

class Myon
{
    public Myon() { }
    public static int Main()
    {
        cin = new Scanner();
        new Myon().calc();
        return 0;
    }

    static Scanner cin;

    // メンバ変数---
    int H;
    int W;
    int A;
    int B;
    const int MOD = 1000000007;
    long[] factorials;
    long[] factorialsInvs;
    // -------------

    void calc()
    {
        

        H = cin.nextInt();
        W = cin.nextInt();
        A = cin.nextInt();
        B = cin.nextInt();

        factorials = new long[100000 * 2];
        factorials[0] = 1;
        factorials[1] = 1;
        for(int i = 2;i < factorials.Length; i++)
        {
            factorials[i] = factorials[i-1] * i % MOD;
        }
        factorialsInvs = new long[100000 * 2];
        factorialsInvs[0] = 1;
        factorialsInvs[1] = 1;
        for (long i = 1; i < factorialsInvs.Length; i++)
        {
            factorialsInvs[i] = ModPow(factorials[i], MOD-2, MOD);
        }

        long a = 0;
        long b = 0;
        long x = 0;
        long y = 0;
        long ret = 0;
        for(long i = B;i < W; i++)
        {
            x = i;
            y = H - A - 1;
            a = cmb(x + y, x);

            x = W - i - 1;
            y = A - 1;
            b = cmb(x + y, x);

            ret += a * b;
            ret %= MOD;
        }

        Write(ret % MOD);
    }

    long cmb(long n, long r)
    {
        if(r < 0 || r > n)
        {
            return 0;
        }
        else
        {
            r = Math.Min(r, n - r);
            return factorials[n] * (factorialsInvs[r] * factorialsInvs[n - r] % MOD) % MOD;
        }
    }


    long ModPow(long a, long n, long mod)
    {
        long res = 1;
        while(n > 0)
        {
            var tmp = n & 1;
            if (tmp == 1)
            {
                res = res * a % MOD;
            }
            a = a * a % mod;
            n = n >> 1;
        }
        return res;
    }

    void Write(string v)
    {
        Console.WriteLine(v);
    }

    void Write(int v)
    {
        Console.WriteLine(v);
    }

    void Write(double v)
    {
        Console.WriteLine(v);
    }
    void Write(long v)
    {
        Console.WriteLine(v);
    }

    int Pow(int x, int y)
    {
        return (int)Math.Pow(double.Parse(x.ToString()), double.Parse(y.ToString()));
    }

    double Pow(double x, double y)
    {
        return Math.Pow(x, y);
    }

    class Scanner
    {
        string[] s;
        int i;

        char[] cs = new char[] { ' ' };

        public Scanner()
        {
            s = new string[0];
            i = 0;
        }

        public string next()
        {
            if (i < s.Length) return s[i++];
            string st = Console.ReadLine();
            while (st == "") st = Console.ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            if (s.Length == 0) return next();
            i = 0;
            return s[i++];
        }

        public int nextInt()
        {
            return int.Parse(next());
        }
        public int[] ArrayInt(int N, int add = 0)
        {
            int[] Array = new int[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt() + add;
            }
            return Array;
        }

        public long nextLong()
        {
            return long.Parse(next());
        }

        public long[] ArrayLong(int N, long add = 0)
        {
            long[] Array = new long[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong() + add;
            }
            return Array;
        }

        public double nextDouble()
        {
            return double.Parse(next());
        }


        public double[] ArrayDouble(int N, double add = 0)
        {
            double[] Array = new double[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextDouble() + add;
            }
            return Array;
        }
    }
}


Measured memory_bytes: 16096