std::relational operators (pair)

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template <class T1, class T2>
 bool operator== (const pair<T1,T2>& lhs, const pair<T1,T2>& rhs)
{ return lhs.first==rhs.first && lhs.second==rhs.second; }
template <class T1, class T2>
 bool operator!= (const pair<T1,T2>& lhs, const pair<T1,T2>& rhs)
{ return !(lhs==rhs); }
template <class T1, class T2>
 bool operator< (const pair<T1,T2>& lhs, const pair<T1,T2>& rhs)
{ return lhs.first<rhs.first || (!(rhs.first<lhs.first) && lhs.second<rhs.second); }
template <class T1, class T2>
 bool operator<= (const pair<T1,T2>& lhs, const pair<T1,T2>& rhs)
{ return !(rhs<lhs); }
template <class T1, class T2>
 bool operator> (const pair<T1,T2>& lhs, const pair<T1,T2>& rhs)
{ return rhs<lhs; }
template <class T1, class T2>
 bool operator>= (const pair<T1,T2>& lhs, const pair<T1,T2>& rhs)
{ return !(lhs<rhs); }

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// pair relational operators
#include <utility> // std::pair
#include <iostream> // std::cout
int main ()
{
 std::pair<int,char> foo (10,'z');
 std::pair<int,char> bar (90,'a');
 if (foo==bar) std::cout << "foo and bar are equal\n";
 if (foo!=bar) std::cout << "foo and bar are not equal\n";
 if (foo< bar) std::cout << "foo is less than bar\n";
 if (foo> bar) std::cout << "foo is greater than bar\n";
 if (foo<=bar) std::cout << "foo is less than or equal to bar\n";
 if (foo>=bar) std::cout << "foo is greater than or equal to bar\n";
 return 0;
}

foo and bar are not equal
foo is less than bar
foo is less than or equal to bar