foo.cc: In function 'void Merge(Node*, Node*)':
foo.cc:48:30: warning: left operand of comma operator has no effect [-Wunused-value]
   48 |         for(p=head1,q=head2;p!=NULL,q!=NULL;)
      |                              ^
foo.cc: In function 'void Unique(Node*, Node*)':
foo.cc:105:18: warning: unused variable 'q' [-Wunused-variable]
  105 |         Node *p,*q;
      |                  ^

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