#include<bits/stdc++.h>
using namespace std;using ll=long long;using vi=vector<int>;using vvi=vector<vi>;using vl=vector<ll>;using vvl=vector<vl>;using P=pair<int,int>;using PL=pair<ll,ll>;using vp=vector<P>;using vpl=vector<PL>;
template<typename T>constexpr auto inf=numeric_limits<T>::max()/2;constexpr int INF=inf<int>,MOD=1000000007;constexpr ll LINF=inf<ll>;
#define _ol3(_1,_2,_3,name,...)name
#define _rep(i,n)_repi(i,0,n)
#define _repi(i,a,b)for(int i=a,i##_l=(b);i<i##_l;++i)
#define REP(...)_ol3(__VA_ARGS__,_repi,_rep,)(__VA_ARGS__)
#define REPR(i,n)for(int i=n-1;i>=0;--i)
#define REPA(i,v)REP(i,(v).size())
#define all(v)(v).begin(),(v).end()
#define rall(v)(v).rbegin(),(v).rend()
#define bit(n)(1ll<<(n))
#define F first
#define S second
#define endl '\n'
#define cho(n,a,b)cout<<((n)?a:b)<<endl
void YES(int n){cho(n,"YES","NO");}void Yes(int n){cho(n,"Yes","No");}void Poss(int n){cho(n,"Possible","Impossible");}
void _print(ostream&){}template<class T,class...U>void _print(ostream&s,const T&t,const U&...u){s<<t<<(sizeof...(u)?' ':'\n');_print(s,u...);}
template<class...T>void print(const T&...t){_print(cout,t...);}template<class...T>void dprint(const T&...t){_print(cerr,t...);}
#ifndef LOCAL
struct osd{template<class T>osd&operator<<(const T&t){return*this;}};osd cer_;
#define dprint(...)
#define cerr cer_
#endif
template<class T>bool chmax(T&a,const T&b){bool x=a<b;x?a=b:b;return x;}template<class T>bool chmin(T&a,const T&b){bool x=a>b;x?a=b:b;return x;}
template<class T,class U>ostream&operator<<(ostream&o,const pair<T,U>&p){return o<<p.F<<' '<<p.S;}
template<class T,class U>istream&operator>>(istream&i,pair<T,U>&p){return i>>p.F>>p.S;}
template<class T>class iterable{static false_type c(string v);template<class U>static auto c(U v)->decltype(all(v),true_type());static false_type c(...);public:const static bool value=decltype(c(declval<T>()))::value;};
template<class T,typename=enable_if_t<iterable<T>::value>>ostream&operator<<(ostream&o,const T&v){for(auto&&i:v)o<<i<<' ';return o;}
template<class T>istream&operator>>(istream&i,vector<T>&v){for(T&j:v)i>>j;return i;}
template<class T>vector<T>&operator<<(vector<T>&v,const T&t){v.push_back(t);return v;}
template<class T>set<T>&operator<<(set<T>&v,const T&t){v.insert(t);return v;}
template<class T>multiset<T>&operator<<(multiset<T>&v,const T&t){v.insert(t);return v;}

inline ll square(ll a){a%=MOD;return (a*a)%MOD;}
ll pow(ll a,ll b){
    a%=MOD;
    b%=MOD-1;
    if(b==0)return 1;
    if(b==1)return a;
    if(b%2){
        return (square(pow(a,b/2)%MOD)*a)%MOD;
    }else{
        return square(pow(a,b/2)%MOD);
    }
}

vector<ll> fact(200001);
vector<ll> facr(200001);


/*ll fact(ll n){
    ll N=n;
    ll ans=1;
    while(n){
        if(fact_cache.find(n)!=fact_cache.end())return (ans*fact_cache.at(n))%MOD;
        ans=(ans*n--)%MOD;
    }
    fact_cache[N]=ans;
    return ans;
}*/

ll factto(ll a,ll b){
    return (fact[b]*facr[a-1])%MOD;
    ll ans=1;
    for(ll i=a;i<=b;i++){
        ans=(ans*i)%MOD;
    }
    return ans;
}

ll perm(ll n,ll r){ // nPr
    return factto(n-r+1,n)%MOD;
}

ll comb(ll n,ll r){ // nCr
    return (perm(n,r)*facr[r])%MOD;
}

ll homo(ll n,ll r){ // nHr
    return comb(n+r-1,r);
}

int main(){
    cin.tie(0);ios::sync_with_stdio(0);
    fact[0]=1;
    REP(i,1,200001)fact[i]=(fact[i-1]*i)%MOD;
    facr[200000]=pow(fact[200000],(ll)MOD-2)%MOD;
    REPR(i,200000)facr[i]=(facr[i+1]*(i+1))%MOD;
    ll h,w,a,b;
    ll ans=0;
    cin>>h>>w>>a>>b;
    REP(i,b,w){
        ans+=(comb(h-a+i-1, i)*comb(a-1+w-i-1, a-1))%MOD;
        ans%=MOD;
        //dprint(i,':',h-a-1,i,',',a-1,w-i-1);
    }
    cout<<ans<<endl;
}


Measured memory_bytes: 3328