In file included from /usr/include/c++/6/bits/char_traits.h:39:0,
                 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_algobase.h: In instantiation of 'const _Tp& std::max(const _Tp&, const _Tp&, _Compare) [with _Tp = int; _Compare = int]':
/in/foo.cc:34:68:   required from here
/usr/include/c++/6/bits/stl_algobase.h:268:17: error: '__comp' cannot be used as a function
       if (__comp(__a, __b))
           ~~~~~~^~~~~~~~~~