View Compilation Error

0_0_39670105_26133.cpp:7:1: error: 'rule' declared as function returning a function
    7 | bool rule() (const int & a, const int & b) const {
      | ^~~~
0_0_39670105_26133.cpp: In function 'int main()':
0_0_39670105_26133.cpp:15:28: error: 'rule' was not declared in this scope
   15 |                 sort(a,a+n,rule);
      |                            ^~~~