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$obj->isa( TYPE ), CLASS->isa( TYPE ), isa( VAL, TYPE )

   use UNIVERSAL qw( isa ) ;
   $yes = isa $h, "HASH";
   $yes = isa "Foo", "Bar";

These subroutines should not be imported via use UNIVERSAL qw(...). 
If you want simple local access to them you can do
...
  *isa = \&UNIVERSAL::isa;

to import isa into your package.