[(if ,test ,conseq ,altern)
         (let-values ([(new-test test-offset) (Pred test fp-offset)])
           (let-values ([(new-conseq conseq-offset) (Tail conseq test-offset)]
                        [(new-altern altern-offset) (Tail altern test-offset)])             
             (values
               `(if ,new-test ,new-conseq ,new-altern)
               fp-offset)))]