#include<iostream>
#include<set>
#include<vector>
#include<functional>
 
int32_t main(void){
 
	std::vector < std::pair<int,int> >  v = { {1,2} , {1,2} };
 
	std::function<bool(int, int)> func = [&v](int i, int j) { return v[i] > v[j]; };
 
	std::set<int, decltype(func)> index_set(func);
 
	index_set.insert(0);
	index_set.insert(1);
 
	std::cout<< "Why is set size equal to " <<  index_set.size() << ". Keys ({0,1}) inserted are not equivalent.\n"; 
	// Why is size still 1?
 
return 0;
}

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