The 'if' special form evaluates the 'test-expr'. If 'test-expr' evaluates
to a non-NIL value, then 'then-expr' is
evaluated and returned as the result. If 'test-expr' evaluates to
NIL and there is an 'else-expr', then the
'else-expr' is evaluated and its result is returned. If there is no
'else-expr' and 'test-expr' evaluates to
(if T (print "will print")     ; prints  "will print"
      (print "won't print"))
(if NIL (print "won't print")
        (print "will print"))  ; prints  "will print"
(if 'a T NIL)                  ; returns T
(if NIL 'nope 'yep)            ; returns YEP
See the
 if 
special form in the