#include<iostream>
#include<vector>
#include<algorithm>
#include<set>
#include<map>
#include<unordered_map>
#include<stack>
#include<queue>
#include<iomanip>
#include<math.h>
#include<bitset>
#include<cassert>
#include<random>
#include<time.h>
#include<functional>
using namespace std;
using ll=long long;
using ld=long double;
using pint=pair<int,int>;
using pll=pair<ll,ll>;
#define MOD 1000000007LL
#define INF 1000000000LL
#define EPS 1e-10
#define FOR(i,n,m) for(ll i=n;i<(ll)m;i++)
#define REP(i,n) FOR(i,0,n)
#define DUMP(a) REP(d,a.size()){cout<<a[d];if(d!=a.size()-1)cout<<" ";else cout<<endl;}
#define ALL(v) v.begin(),v.end()
#define UNIQUE(v)  sort(ALL(v));v.erase(unique(ALL(v)),v.end());
#define pb push_back

#define MAX_N 1000100
long long extgcd(long long a, long long b, long long& x, long long& y) {
	long long d = a;
	if (b != 0) {
		d = extgcd(b, a % b, y, x);
		y -= (a / b) * x;
	} else {
		x = 1; y = 0;
	}
	return d;
}
long long mod_inverse(long long a, long long m) {
	long long x, y;
	if(extgcd(a, m, x, y) == 1) return (m + x % m) % m;
	else return -1;
}
vector<long long> fact(MAX_N+1, INF);
long long mod_fact(long long n, long long& e) {
	if(fact[0] == INF) {
		fact[0]=1;
		if(MAX_N != 0) fact[1]=1;
		for(ll i = 2; i <= MAX_N; ++i) {
			fact[i] = (fact[i-1] * i) % MOD;
		}
	}
	e = 0;
	if(n == 0) return 1;
	long long res = mod_fact(n / MOD, e);
	e += n / MOD;
	if((n / MOD) % 2 != 0) return (res * (MOD - fact[n % MOD])) % MOD;
	return (res * fact[n % MOD]) % MOD;
}
// return nCk
long long mod_comb(long long n, long long k) {
	if(n < 0 || k < 0 || n < k) return 0;
	long long e1, e2, e3;
	long long a1 = mod_fact(n, e1), a2 = mod_fact(k, e2), a3 = mod_fact(n - k, e3);
	if(e1 > e2 + e3) return 0;
	return (a1 * mod_inverse((a2 * a3) % MOD, MOD)) % MOD;
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	ll n, m;
	cin >> n >> m;
	vector<ll> modpow(2020, 0);
	modpow[0] = modpow[1] = 1;
	FOR(i, 2, 2020) {
		modpow[i] = i * modpow[i - 1];
		modpow[i] %= MOD;
	}
	vector<ll> a(n);
	vector<ll> b(m);
	REP(i, n) cin >> a[i];
	REP(i, m) cin >> b[i];
	REP(i, n) FOR(j, i + 1, n) {
		if(a[i] == a[j]) {
			cout << 0 << endl;
			return 0;
		}
	}
	REP(i, m) FOR(j, i + 1, m) {
		if(b[i] == b[j]) {
			cout << 0 << endl;
			return 0;
		}
	}
	vector<pll> v;
	REP(i, n) v.pb(pll(a[i], 0));
	REP(i, m) v.pb(pll(b[i], 1));
	sort(ALL(v));
	ll ans = 1;
	ll rem1 = n, rem2 = m;
	ll used = 0;
	REP(i, v.size()) {
		if(i < (ll)v.size() - 1 && v[i].first == v[i + 1].first) {
			if(v[i].first - used < rem1 + rem2 - 1) {
				cout << 0 << endl;
				return 0;
			}
			ans *= (modpow[rem1 + rem2 - 2] * mod_comb(v[i].first - used - 1, rem1 + rem2 - 2)) % MOD;
			ans %= MOD;
			used += rem1 + rem2 - 1;
			rem1--;
			rem2--;
			i++;
		} else {
			if(v[i].second == 0) {
				if(v[i].first - used < rem2) {
					cout << 0 << endl;
					return 0;
				}
				ans *= (modpow[rem2] * mod_comb(v[i].first - used - 1, rem2 - 1)) % MOD;
				ans %= MOD;
				used += rem2;
				rem1--;
			} else {
				if(v[i].first - used < rem1) {
					cout << 0 << endl;
					return 0;
				}
				ans *= (modpow[rem1] * mod_comb(v[i].first - used - 1, rem1 - 1)) % MOD;
				ans %= MOD;
				used += rem1;
				rem2--;
			}
		}
	}
	cout << ans << endl;
	return 0;
}

/* --------------------------------------- */


Measured memory_bytes: 8192