foo.cc: In function 'bool pn(int)':
foo.cc:16:7: warning: variable 'y' set but not used [-Wunused-but-set-variable]
   16 |  bool y=true;
      |       ^
foo.cc:25:1: warning: no return statement in function returning non-void [-Wreturn-type]
   25 | }
      | ^

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