foo.cpp: In function 'void work(int, int, int, int)':
foo.cpp:57:6: error: reference to 'hash' is ambiguous
  ins(hash());
      ^
foo.cpp:45:11: note: candidates are: LL hash()
 inline LL hash()
           ^
In file included from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\basic_string.h:3033:0,
                 from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\string:52,
                 from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\locale_classes.h:40,
                 from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\ios_base.h:41,
                 from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\ios:42,
                 from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\ostream:38,
                 from c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\iostream:39,
                 from foo.cpp:3:
c:\mingw\lib\gcc\mingw32\4.8.1\include\c++\bits\functional_hash.h:58:12: note:                 template<class _Tp> struct std::hash
     struct hash;
            ^