/in/foo.cc: In function 'void add(int, int, int, int, int, int)':
/in/foo.cc:66:6: error: reference to 'hash' is ambiguous
  if (hash[x1][y1][x2][y2][t]) return;
      ^~~~
/in/foo.cc:8:6: note: candidates are: bool hash [20][20][20][20][4]
 bool hash[20][20][20][20][4];
      ^~~~
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/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:2:
/usr/include/c++/6/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^~~~
/in/foo.cc:67:2: error: reference to 'hash' is ambiguous
  hash[x1][y1][x2][y2][t] = 1;
  ^~~~
/in/foo.cc:8:6: note: candidates are: bool hash [20][20][20][20][4]
 bool hash[20][20][20][20][4];
      ^~~~
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/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:2:
/usr/include/c++/6/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:86:9: error: reference to 'hash' is ambiguous
  memset(hash,0,sizeof(hash));
         ^~~~
/in/foo.cc:8:6: note: candidates are: bool hash [20][20][20][20][4]
 bool hash[20][20][20][20][4];
      ^~~~
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/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:2:
/usr/include/c++/6/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^~~~
/in/foo.cc:86:23: error: reference to 'hash' is ambiguous
  memset(hash,0,sizeof(hash));
                       ^~~~
/in/foo.cc:8:6: note: candidates are: bool hash [20][20][20][20][4]
 bool hash[20][20][20][20][4];
      ^~~~
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/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:2:
/usr/include/c++/6/bits/functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^~~~