foo.cc: In function 'Node* Unique(Node*)':
foo.cc:67:32: warning: variable 'prev1' set but not used [-Wunused-but-set-variable]
   67 |         Node* p1 = new Node, * prev1 = new Node;
      |                                ^~~~~
foo.cc: In function 'Node* SetUnion(Node*, Node*)':
foo.cc:81:43: warning: variable 'prev1' set but not used [-Wunused-but-set-variable]
   81 |         Node* p1 = head1, * p2 = head2, * prev1 = NULL, * prev2 = NULL;
      |                                           ^~~~~

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