View Compilation Error

0_0_29993205_501.cpp:11:22: error: 'nd' does not name a type
 bool operator<(const nd &a, const nd &b) { return a.x < b.x; }
                      ^
0_0_29993205_501.cpp:11:35: error: 'nd' does not name a type
 bool operator<(const nd &a, const nd &b) { return a.x < b.x; }
                                   ^
0_0_29993205_501.cpp:11:40: error: 'bool operator<(const int&, const int&)' must have an argument of class or enumerated type
 bool operator<(const nd &a, const nd &b) { return a.x < b.x; }
                                        ^