Compilare: user.cpp: In instantiation of ‘std::size_t pair_hash::operator()(const std::pair<_T1, _T2>&) const [with T1 = int; T2 = int; std::size_t = unsigned int]’: /usr/include/c++/4.8/bits/hashtable_policy.h:1103:22: required from ‘std::__detail::_Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, std::__detail::_Default_ranged_hash, true>::__hash_code std::__detail::_Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, std::__detail::_Default_ranged_hash, true>::_M_hash_code(const _Key&) const [with _Key = std::pair<int, int>; _Value = std::pair<const std::pair<int, int>, int>; _ExtractKey = std::__detail::_Select1st; _H1 = pair_hash; _H2 = std::__detail::_Mod_range_hashing; std::__detail::_Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, std::__detail::_Default_ranged_hash, true>::__hash_code = unsigned int]’ /usr/include/c++/4.8/bits/hashtable.h:1023:50: required from ‘std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, _Traits>::iterator std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, _Traits>::find(const key_type&) [with _Key = std::pair<int, int>; _Value = std::pair<const std::pair<int, int>, int>; _Alloc = std::allocator<std::pair<const std::pair<int, int>, int> >; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<int, int> >; _H1 = pair_hash; _H2 = std::__detail::_Mod_range_hashing; _Hash = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<true, false, true>; std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, _Traits>::iterator = std::__detail::_Node_iterator<std::pair<const std::pair<int, int>, int>, false, true>; std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, _Traits>::key_type = std::pair<int, int>]’ /usr/include/c++/4.8/bits/unordered_map.h:543:29: required from ‘std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::iterator std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::find(const key_type&) [with _Key = std::pair<int, int>; _Tp = int; _Hash = pair_hash; _Pred = std::equal_to<std::pair<int, int> >; _Alloc = std::allocator<std::pair<const std::pair<int, int>, int> >; std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::iterator = std::__detail::_Node_iterator<std::pair<const std::pair<int, int>, int>, false, true>; std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::key_type = std::pair<int, int>]’ user.cpp:40:27: required from here user.cpp:22:14: warning: unused variable ‘h1’ [-Wunused-variable] auto h1 = std::hash<T1>{}(p.first); ^ user.cpp:23:14: warning: unused variable ‘h2’ [-Wunused-variable] auto h2 = std::hash<T2>{}(p.second); ^