View Compilation Error

0_0_18723769_8944.cpp: In function 'bool fun(int, int, int, int)':
0_0_18723769_8944.cpp:10:24: error: 'ck' was not declared in this scope
   if(ck(a-1,b-1,c-1,d-1)) return true;
                        ^
0_0_18723769_8944.cpp:13:22: error: 'ck' was not declared in this scope
   if(ck(a-1,b-1,c-1,d)) return true;
                      ^
0_0_18723769_8944.cpp:16:22: error: 'ck' was not declared in this scope
   if(ck(a,b-1,c-1,d-1)) return true;
                      ^