#include <iostream>
#include <utility>
#include <algorithm>
#include <set>
using namespace std;
 
using OP = pair<unsigned, unsigned>;
using SOP = set<OP>; 
 
bool is_symetric (SOP sop) {
    return all_of(sop.cbegin(), sop.cend(),
        [&sop](auto &x){ return x.first==x.second || sop.find({x.second,x.first })!=sop.end();}) ;
}
 
int main() {
	SOP test1 { {1,3},{2,4},{5,7},{7,5}, {4,2}, {3,1} };
	SOP test2 { {1,3},{2,4},{5,7},{7,5}, {4,2}, {3,1}, {8,4} };
 
	cout << is_symetric(test1)<<endl; 
	cout << is_symetric(test2)<<endl; 
	return 0;
}

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