Language: C++

    // need
    #include <iostream>
    #include <algorithm>
    // data structure
    #include <bitset>
    #include <map>
    #include <queue>
    #include <set>
    #include <stack>
    #include <string>
    #include <utility>
    #include <vector>
    #include <complex>
    //#include <deque>
    #include <valarray>
    #include <unordered_map>
    #include <unordered_set>
    #include <array>
    // stream
    //#include <istream>
    #include <sstream>
    //#include <ostream>
    #include <fstream>
    // etc
    #include <cassert>
    #include <cmath>
    #include <functional>
    #include <iomanip>
    //#include <chrono>
    #include <random>
    #include <numeric>
     
    // input
    #define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
    #define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
    template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
    template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest&...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
    #define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int w_=0; w_<n; ++w_){MACRO_VEC_ROW_Scan(w_, __VA_ARGS__);}
    template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
    template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest&...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
    template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
    template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest&...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
    #define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
    #define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& R:c)for(auto& w:R)std::cin>>w;
    // output
    #define OUT(dist) std::cout<<(dist);
    #define FOUT(n, dist) std::cout<<std::fixed<<std::setprecision(n)<<(dist);
    #define SOUT(n, c, dist) std::cout<<std::setw(n)<<std::setfill(c)<<(dist);
    #define SP std::cout<<" ";
    #define TAB std::cout<<"\t";
    #define BR std::cout<<"\n";
    #define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
    #define ENDL std::cout<<std::endl;
    #define FLUSH std::cout<<std::flush;
    #define SHOW(dist) {std::cerr << #dist << "\t:" << (dist) << "\n";}
    #define SHOWVECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
    #define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
    #define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t:";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}
    // utility
    #define ALL(a) (a).begin(),(a).end()
    #define FOR(w, a, n) for(int w=(a);w<(n);++w)
    #define RFOR(w, a, n) for(int w=(n)-1;w>=(a);--w)
    #define REP(w, n) for(int w=0;w<int(n);++w)
    #define RREP(w, n) for(int w=int(n)-1;w>=0;--w)
    #define FORLL(w, a, n) for(ll w=ll(a);w<ll(n);++w)
    #define RFORLL(w, a, n) for(ll w=ll(n)-1;w>=ll(a);--w)
    #define REPLL(w, n) for(ll w=0;w<ll(n);++w)
    #define RREPLL(w, n) for(ll w=ll(n)-1;w>=0;--w)
    #define IN(a, x, b) (a<=x && x<b)
    template<class T> inline T CHMAX(T& a, const T b) { return a = (a < b) ? b : a; }
    template<class T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
    #define EXCEPTION(msg) throw std::string("Exception : " msg " [ in ") + __func__ + " : " + std::to_string(__LINE__) + " lines ]"
    #define TRY(cond, msg) try {if (cond) EXCEPTION(msg);}catch (std::string s) {std::cerr << s << std::endl;}
    //void CHECKTIME(std::function<void()> f) { auto start = std::chrono::system_clock::now(); f(); auto end = std::chrono::system_clock::now(); auto res = std::chrono::duration_cast<std::chrono::nanoseconds>((end - start)).count(); std::cerr << "[Time:" << res << "ns  (" << res / (1.0e9) << "s)]\n"; }
    // test
    template<class T> std::vector<std::vector<T>> VV(int n, int m, T init = T()) {
    	return std::vector<std::vector<T>>(n, std::vector<T>(m, init));
    }
    template<typename S, typename T>
    std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
    	os << "(" << p.first << ", " << p.second << ")"; return os;
    }
     
    // type/const
    #define int ll
    using ll = long long;
    using ull = unsigned long long;
    using ld = long double;
    using PAIR = std::pair<int, int>;
    using PAIRLL = std::pair<ll, ll>;
    constexpr int INFINT = 1 << 30;                          // 1.07x10^ 9
    constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
    constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
    constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
    constexpr double EPS = 1e-10;
    constexpr int MOD = 1000000007;
    constexpr double PI = 3.141592653589793238462643383279;
    template<class T, size_t N> void FILL(T(&a)[N], const T& val) { for (auto& x : a) x = val; }
    template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T& val) { for (auto& b : a) FILL(b, val); }
    template<class T> void FILL(std::vector<T>& a, const T& val) { for (auto& x : a) x = val; }
    template<class ARY, class T> void FILL(std::vector<std::vector<ARY>>& a, const T& val) { for (auto& b : a) FILL(b, val); }
    // ------------>8------------------------------------->8------------
     
     
     
    signed main() {
    	INIT;
     
    	VAR(int, n, m);
    	VEC(int, a, n);
    	VEC(int, b, m);
     
    	std::sort(ALL(a)); std::reverse(ALL(a));
    	std::sort(ALL(b)); std::reverse(ALL(b));
     
    	const int M = n * m;
     
    	std::vector<PAIR> pos(M + 1, PAIR(-INFINT, -INFINT));
     
    	REP(i, n) {
    		if (pos[a[i]].first != -INFINT) {
    			OUT(0)BR;
    			return 0;
    		}
    		pos[a[i]].first = i;
    	}
    	REP(j, m) {
    		if (pos[b[j]].second != -INFINT) {
    			OUT(0)BR;
    			return 0;
    		}
    		pos[b[j]].second = j;
    	}
     
    	if (pos[M].first == -INFINT || pos[M].second == -INFINT) {
    		OUT(0)BR;
    		return 0;
    	}
     
    	int p = 0, q = 0;
    	int ans = 1;
    	int rest = 0;
     
    	RFOR(i, 1, M) {
    		bool P = pos[i].first == p + 1;
    		bool Q = pos[i].second == q + 1;
     
    		if(P) {
    			++p;
    			rest += q + 1;
    		}
    		if(Q) {
    			++q;
    			rest += p + 1;
    		}
    		if (P && Q);
    		else if (P) (ans *= q + 1) %= MOD;
    		else if (Q) (ans *= p + 1) %= MOD;
    		else (ans *= rest) %= MOD;
    		--rest;
    		if (rest < 0) ans = 0;
            std::err < rest <<std::endl;
    	}
    	OUT(ans)BR;
    	return 0;
    }

Compiler output:
a.cc: In function 'int main()':
a.cc:162:18: error: 'err' is not a member of 'std'; did you mean 'errc'?
  162 |             std::err < rest <<std::endl;
      |                  ^~~
      |                  errc
a.cc:162:29: error: invalid operands of types 'll' {aka 'long long int'} and '<unresolved overloaded function type>' to binary 'operator<<'
  162 |             std::err < rest <<std::endl;
      |                        ~~~~~^~~~~~~~~~~