#include <iostream>
#include <cstdint>
#include <utility>
#include <tuple>
#include <vector>
#include <stack>
#include <queue>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
#include <limits>
#include <numeric>
#include <iomanip>

using namespace std;

// Type aliases
using i8  =  int8_t; using  u8 =  uint8_t;
using i16 = int16_t; using u16 = uint16_t;
using i32 = int32_t; using u32 = uint32_t;
using i64 = int64_t; using u64 = uint64_t;

template <class T> using V = vector<T>;

// Loops
#define REP(i, n) for (i64 i = 0; i < (n); ++i)
#define REPR(i, n) for (i64 i = (n) - 1; i >= 0; --i)
#define FOR(i, n, m) for (i64 i = (n); i < (m); ++i)
#define FORR(i, n, m) for (i64 i = (m) - 1; i >= (n); --i)

#define FORE(x, xs) for (auto &x: (xs))

// Macros
#define CTR(x) (x).begin(), (x).end()

// Utils for Tuple
namespace tuple_utils {
    template<size_t...> struct seq{};

    template<size_t N, size_t... Is>
    struct gen_seq : gen_seq<N - 1, N - 1, Is...>{};

    template<size_t... Is>
    struct gen_seq<0, Is...> : seq<Is...>{};

    template <class Tuple, size_t... Is>
    void read(istream &stream, Tuple &t, seq<Is...>) {
        static_cast<void>((int[]){0, (void(stream  >> get<Is>(t)), 0)...});
    }

    template<class Tuple, size_t... Is>
    void print(ostream& stream, Tuple const& t, seq<Is...>) {
        static_cast<void>((int[]){0, (void(stream << (Is == 0 ?  "" : ", ") << get<Is>(t)), 0)...});
    }

    template <size_t I, class F, class A, class... Elems>
    struct ForEach {
        void operator()(A &arg, tuple<Elems...> const& t) const {
            F()(arg, get<I>(t));
            ForEach<I - 1, F, A, Elems...>()(arg, t);
        };
        void operator()(A &arg, tuple<Elems...>& t) const {
            F()(arg, get<I>(t));
            ForEach<I - 1, F, A, Elems...>()(arg, t);
        };
    };
    template <class F, class A, class... Elems>
    struct ForEach<0, F, A, Elems...> {
        void operator()(A &arg, tuple<Elems...> const& t) const {
            F()(arg, get<0>(t));
        };
        void operator()(A &arg, tuple<Elems...>& t) const {
            F()(arg, get<0>(t));
        };
    };
    template <class F, class A, class... Elems>
    void for_each(A &arg, tuple<Elems...> const& t) {
        ForEach<tuple_size<tuple<Elems...>>::value - 1, F, A, Elems...>()(arg, t);
    };
    template <class F, class A, class... Elems>
    void for_each(A &arg, tuple<Elems...>& t) {
        ForEach<tuple_size<tuple<Elems...>>::value - 1, F, A, Elems...>()(arg, t);
    };

    struct hash_for_element {
        template <class V>
        void operator()(size_t &size, const V& v) const {
            size ^= hash<V>()(v);
        }
    };
}

// STL support
template <class Iterator>
struct Container {
    Container(const Iterator &begin, const Iterator &end) : m_begin(begin), m_end(end) {}
    const Iterator& begin() const {
        return this->m_begin;
    }
    const Iterator& end() const {
        return this->m_end;
    }
    Iterator m_begin;
    Iterator m_end;
};

template <class Functions>
struct BaseIterator {
    using State = typename Functions::State;

    BaseIterator(const State &state, const Functions &func) : state(state), func(func) {
        while (!this->is_end() && !this->is_valid()) {
            this->next();
        }
    }
    BaseIterator(const State &state) : state(state), func() {
        while (!this->is_end() && !this->is_valid()) {
            this->next();
        }
    }

    decltype(auto) operator*() {
        return this->func.get_value(this->state);
    }

    decltype(auto) operator*() const {
        return this->func.get_value(this->state);
    }

    BaseIterator &operator++() {
        if (this->is_end()) {
            return *this;
        }

        this->next();
        while (!this->is_end() && !this->is_valid()) {
            this->next();
        }

        return *this;
    }

    BaseIterator &operator--() {
        if (this->is_begin()) {
            return *this;
        }

        this->previous();
        while (!this->is_begin() && !this->is_valid()) {
            this->previous();
        }

        return *this;
    }

    bool operator==(const BaseIterator<Functions> &rhs) const {
        return this->state == rhs.state;
    }
    bool operator!=(const BaseIterator<Functions> &rhs) const {
        return !(*this == rhs);
    }

    bool is_begin() const {
        return this->func.is_begin(this->state);
    }
    bool is_end() const {
        return this->func.is_end(this->state);
    }
    const State &get_state() const {
        return this->state;
    }
private:
    bool is_valid() const {
        return this->func.is_valid(this->state);
    }
    void next() {
        this->func.next(this->state);
    }
    void previous() {
        this->func.previous(this->state);
    }
    State state;
    Functions func;
};

// Input
template <class F, class S>
istream &operator>>(istream &stream, pair<F, S> &pair) {
    stream >> pair.first;
    stream >> pair.second;
    return stream;
}
template <class ...Args>
istream &operator>>(istream &stream, tuple<Args...> &tuple) {
    tuple_utils::read(stream, tuple, tuple_utils::gen_seq<sizeof...(Args)>());
    return stream;
}

template <class T>
T read() {
    T t;
    cin >> t;
    return t;
}
template <class F, class S>
pair<F, S> read() {
    pair<F, S> p;
    cin >> p;
    return p;
}
template <class T1, class T2, class T3, class ...Args>
tuple<T1, T2, T3, Args...> read() {
    tuple<T1, T2, T3, Args...> t;
    cin >> t;
    return t;
}

template <class T>
V<T> read(const int length) {
    V<T> ts(length);
    for (auto& t: ts) {
        cin >> t;
    }
    return ts;
}
template <class F, class S>
V<pair<F, S>> read(const int length) {
    V<pair<F, S>> ps(length);
    for (auto& p: ps) {
        cin >> p;
    }
    return ps;
}
template <class T1, class T2, class T3, class ...Args>
V<tuple<T1, T2, T3, Args...>> read(const int length) {
    V<tuple<T1, T2, T3, Args...>> ts(length);
    for (auto& t: ts) {
        cin >> t;
    }
    return ts;
}

// Output
namespace debug {
    template <class F, class S>
    ostream &operator<<(ostream& stream, const pair<F, S> &pair) {
        stream << "{" << pair.first << ", " << pair.second << "}";
        return stream;
    }
    template <class ...Args>
    ostream &operator<<(ostream& stream, const tuple<Args...> &tuple) {
        stream << "{";
        tuple_utils::print(stream, tuple, tuple_utils::gen_seq<sizeof...(Args)>());
        stream << "}";
        return stream;
    }

    template <class Iterator>
    Container<Iterator> container(const Iterator &begin, const Iterator &end) {
        return Container<Iterator>(begin, end);
    }

    template <class Iterator>
    ostream &operator<<(ostream &stream, const Container<Iterator> &container) {
        stream << "[";

        size_t cnt = 0;
        for (const auto &it: container) {
            stream << it;
            stream << "," << ((cnt % 10 == 9) ? "\n " : "\t");

            cnt += 1;
        }

        stream << "\b\b]";
        return stream;
    }

    template <class T, class Alloc>
    ostream &operator<<(ostream& stream, const vector<T, Alloc> &vector) {
        return stream << container(vector.begin(), vector.end());
    }
}

// Hash
namespace std {
    template <class F, class S>
    struct hash<pair<F, S>> {
        size_t operator ()(const pair<F, S> &p) const {
            return hash<F>()(p.first) ^ hash<S>()(p.second);
        }
    };

    template <class ...Args>
    struct hash<tuple<Args...>> {
        size_t operator ()(const tuple<Args...> &t) const {
            size_t retval = 0;

            tuple_utils::for_each<tuple_utils::hash_for_element, size_t, Args...>(retval, t);

            return retval;
        }
    };
}
#define MAIN
void body();

#ifndef MAIN
#include "common.cc"
#endif

/*
 * n^r
 */
template<class V>
static V pow(V n, i64 r) {
    if (r == 0) {
        return 1;
    }

    auto r2 = r / 2;
    auto x2 = pow(n, r2);

    return x2 * x2 * ((r % 2 == 0) ? 1 : n);
}

static i64 gcd(i64 a, i64 b) {
    if (b == 0) return a;
    return gcd(b, a % b);
}

template<class Iterator>
static i64 gcd_ctr(const Iterator &begin, const Iterator &end) {
    if (begin == end) {
        return -1;
    } else {
        auto ans = *begin;
        auto it = begin;
        ++it;
        for (; it != end; ++it) {
            auto x = *it;
            ans = gcd(ans, x);
        }
        return ans;
    }
}

static i64 gcd_ctr(const V<i64> &xs) {
    return gcd_ctr(xs.begin(), xs.end());
}

static i64 lcm(i64 a, i64 b) {
    auto x = gcd(a, b);
    return a / x * b;
}

template<class Iterator>
static i64 lcm_ctr(const Iterator &begin, const Iterator &end) {
    if (begin == end) {
        return -1;
    } else {
        auto ans = *begin;
        auto it = begin;
        ++it;
        for (; it != end; ++it) {
            auto x = *it;
            ans = lcm(ans, x);
        }
        return ans;
    }
}

static i64 lcm_ctr(const V<i64> &xs) {
    return lcm_ctr(xs.begin(), xs.end());
}

template<class V>
static V combination(V n, i64 r) {
    if (r == 0) {
        return 1;
    }

    V x = 1;
    FOR (d, 1, r + 1) {
        x *= n;
        n -= 1;
        x /= d;
    }
    return x;
}

static bool is_prime(i64 n) {
    if (n <= 1) return false;
    for (i64 i = 2; i * i <= n; i++) {
        if (n % i == 0) return false;
    }
    return true;
}

static V<i64> divisor(i64 n) {
    V<i64> res;
    for (i64 i = 2; i * i <= n; i++) {
        if (n % i == 0) {
            res.push_back(i);
            if (i != n / i) res.push_back(n / i);
        }
    }
    return res;
}

static unordered_map<i64, size_t> prime_factor(i64 n) {
    unordered_map<i64, size_t> res;
    for (i64 i = 2; i * i <= n; i++) {
        while (n % i == 0) {
            res[i] += 1;
            n /= i;
        }
    }
    if (n != 1) res[n] = 1;
    return res;
}

static pair<V<i64>, V<bool>> sieve(i64 n) {
    V<i64> prime;
    V<bool> is_prime_(n + 1, true);
    is_prime_[0] = is_prime_[1] = false;

    FOR (i, 2, n + 1) {
        if (is_prime_[i]) {
            prime.push_back(i);
            for (i64 j = 2 * i; j <= n; j += i) {
                is_prime_[j] = false;
            }
        }
    }
    return {prime, is_prime_};
}

#ifndef MAIN
#include "common.cc"
#include "math.cc"
#endif

namespace mod {
    const i64 MOD = 1000000007;

    struct Integer {
        Integer() : value(0) {}
        Integer(i64 value) {
            update_value((value));
        }

        Integer inverse() const {
            return pow(*this, 1000000005);
        }

        Integer operator+(const Integer &rhs) const {
            return this->value + rhs.value;
        }
        Integer operator-(const Integer &rhs) const {
            return this->value - rhs.value;
        }

        Integer operator*(const Integer &rhs) const {
            return this->value * rhs.value;
        }

        Integer operator /(const Integer &rhs) const {
            return this->value * rhs.inverse().value;
        }

        void operator +=(const Integer &rhs) {
            update_value(this->value + rhs.value);
        }

        void operator -=(const Integer &rhs) {
            update_value(this->value - rhs.value);
        }

        void operator *=(const Integer &rhs) {
            update_value(this->value * rhs.value);
        }

        void operator /=(const Integer &rhs) {
            update_value(this->value * rhs.inverse().value);
        }

        bool operator==(const Integer &rhs) const {
            return this->value == rhs.value;
        }
        template <class V>
        bool operator==(V rhs) const {
            return this->value == rhs;
        }

        bool operator!=(const Integer &rhs) const {
            return this->value != rhs.value;
        }
        template <class V>
        bool operator!=(V rhs) const {
            return this->value != rhs;
        }

        const i64 &get() const {
            return this->value;
        }

    private:
        void update_value(i64 new_value) {
            this->value = new_value;
            if (this->value < 0) {
                this->value += MOD;
            }
            if (this->value >= MOD) {
                this->value %= MOD;
            }
        }
        i64 value;
    };

    template <class V>
    static bool operator==(V lhs, const Integer &rhs) {
        return rhs ==lhs;
    }
    template <class V>
    static bool operator!=(V lhs, const Integer &rhs) {
        return rhs != lhs;
    }

    struct fact {
        Integer value;
        Integer inverse;
    };

    static V<fact> fact_table(const size_t n) {
        V<fact> retval(n + 1);

        retval[0].value = 1;
        FOR(i, 1, n + 1) {
            retval[i].value = retval[i - 1].value * i;
        }

        retval[n].inverse = retval[n].value.inverse();
        REPR(i, n) {
            retval[i].inverse = retval[i + 1].inverse * (i + 1);
        }

        return retval;
    }
}

// main function (DO NOT EDIT)
int main (int argc, char **argv) {
    cin.tie(0);
    ios_base::sync_with_stdio(false);

    cout << fixed;
    body();

    return 0;
}

void body() {
    using namespace debug;
    auto H = read<i64>();
    auto W = read<i64>();
    auto A = read<i64>();
    auto B = read<i64>();

    using namespace mod;

    mod::Integer ans = 0;
    auto table = mod::fact_table((H + W));

    FOR (i, B, W) {
        // (0, 0) -> (H-A-1, i)
        auto r1 = table[H - A - 1 + i].value * table[H - A - 1].inverse * table[i].inverse;
        // (H-A, i) -> (H-1, W-1)
        auto h = A - 1;
        auto w = W - i - 1;
        auto r2 = table[h + w].value * table[h].inverse * table[w].inverse;
        ans += r1 * r2;
    }
    cout << ans.get() << endl;
}

Measured memory_bytes: 3328