In file included from /usr/include/c++/6/string:48:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_function.h: In instantiation of 'bool std::greater<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = node]':
/usr/include/c++/6/bits/predefined_ops.h:147:11:   required from 'bool __gnu_cxx::__ops::_Iter_comp_val<_Compare>::operator()(_Iterator, _Value&) [with _Iterator = __gnu_cxx::__normal_iterator<node*, std::vector<node> >; _Value = node; _Compare = std::greater<node>]'
/usr/include/c++/6/bits/stl_heap.h:129:48:   required from 'void std::__push_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<node*, std::vector<node> >; _Distance = long int; _Tp = node; _Compare = __gnu_cxx::__ops::_Iter_comp_val<std::greater<node> >]'
/usr/include/c++/6/bits/stl_heap.h:201:23:   required from 'void std::push_heap(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<node*, std::vector<node> >; _Compare = std::greater<node>]'
/usr/include/c++/6/bits/stl_queue.h:569:16:   required from 'void std::priority_queue<_Tp, _Sequence, _Compare>::push(std::priority_queue<_Tp, _Sequence, _Compare>::value_type&&) [with _Tp = node; _Sequence = std::vector<node>; _Compare = std::greater<node>; std::priority_queue<_Tp, _Sequence, _Compare>::value_type = node]'
/in/foo.cc:31:27:   required from here
/usr/include/c++/6/bits/stl_function.h:376:20: error: no match for 'operator>' (operand types are 'const node' and 'const node')
       { return __x > __y; }
                ~~~~^~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:64:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_pair.h:454:5: note: candidate: template<class _T1, class _T2> constexpr bool std::operator>(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
     operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
     ^~~~~~~~
/usr/include/c++/6/bits/stl_pair.h:454:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/string:48:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_function.h:376:20: note:   'const node' is not derived from 'const std::pair<_T1, _T2>'
       { return __x > __y; }
                ~~~~^~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:310:5: note: candidate: template<class _Iterator> bool std::operator>(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
     operator>(const reverse_iterator<_Iterator>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:310:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/string:48:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_function.h:376:20: note:   'const node' is not derived from 'const std::reverse_iterator<_Iterator>'
       { return __x > __y; }
                ~~~~^~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:367:5: note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator>(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&)
     operator>(const reverse_iterator<_IteratorL>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:367:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/string:48:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_function.h:376:20: note:   'const node' is not derived from 'const std::reverse_iterator<_Iterator>'
       { return __x > __y; }
                ~~~~^~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:1161:5: note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator>(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorR>&)
     operator>(const move_iterator<_IteratorL>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:1161:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/string:48:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_function.h:376:20: note:   'const node' is not derived from 'const std::move_iterator<_IteratorL>'
       { return __x > __y; }
                ~~~~^~~~~
In file included from /usr/include/c++/6/bits/stl_algobase.h:67:0,
                 from /usr/include/c++/6/bits/char_traits.h:39,
                 from /usr/include/c++/6/ios:40,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_iterator.h:1167:5: note: candidate: template<class _Iterator> bool std::operator>(const std::move_iterator<_IteratorL>&, const std::move_iterator<_IteratorL>&)
     operator>(const move_iterator<_Iterator>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/stl_iterator.h:1167:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/6/string:48:0,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/stl_function.h:376:20: note:   'const node' is not derived from 'const std::move_iterator<_IteratorL>'
       { return __x > __y; }
                ~~~~^~~~~
In file included from /usr/include/c++/6/