/in/foo.cc: In function 'int main()':
/in/foo.cc:54:6: error: reference to 'hash' is ambiguous
    p[hash(i,j)]=true;
      ^~~~
/in/foo.cc:36:27: note: candidates are: long long unsigned int hash(int, int)
 inline unsigned long long hash(int x,int y) {
                           ^~~~
In file included from /usr/include/c++/6/bits/basic_string.h:5643:0,
                 from /usr/include/c++/6/string:52,
                 from /usr/include/c++/6/stdexcept:39,
                 from /usr/include/c++/6/array:39,
                 from /usr/include/c++/6/tuple:39,
                 from /usr/include/c++/6/bits/stl_map.h:63,
                 from /usr/include/c++/6/map:61,
                 from /in/foo.cc:2:
/usr/include/c++/6/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^~~~