/in/foo.cc: In function 'int main()':
/in/foo.cc:208:8: warning: unused variable 'head1' [-Wunused-variable]
  Node* head1 = Create(a1, n1);
        ^~~~~
/in/foo.cc:209:8: warning: unused variable 'head2' [-Wunused-variable]
  Node* head2 = Create(a2, n2);
        ^~~~~
/in/foo.cc:210:8: warning: unused variable 'head3' [-Wunused-variable]
  Node* head3 = Create(a3, n3);
        ^~~~~
/in/foo.cc:211:8: warning: unused variable 'head12' [-Wunused-variable]
  Node* head12 = NULL;
        ^~~~~~
/in/foo.cc:212:8: warning: unused variable 'head13' [-Wunused-variable]
  Node* head13 = NULL;
        ^~~~~~