It is not always easy to be certain that transformed code will give exactly the same results.
( (> (* ?n ?x)
(* ?n ?y)) (> ?x ?y) )
( (not (not ?x)) ?x )
( (eq (if ?p ?qu ?qv)
?qu) ?p )
( (rplaca ?x ?y) (setf (car ?x) ?y) )
These transformations are ``usually'' correct, but it is possible to construct an example for each in which the transformation changes the result. We must be careful to use only correct transforms.