• not x → boolean

• x - a generalized boolean (i.e. any object).
• boolean - a boolean.

Returns t if x is false; otherwise, returns nil.

(not nil) 

→

T



(not '()) 

→

T



(not (integerp 'sss)) 

→

T



(not (integerp 1)) 

→

NIL



(not 3.7) 

→

NIL



(not 'apple) 

→

NIL

None.

None.

None.

• Function NULL

not is intended to be used to invert the `truth value' of a boolean (or generalized boolean) whereas null is intended to be used to test for the empty list. Operationally, not and null compute the same result; which to use is a matter of style.

\issue{NOT-AND-NULL-RETURN-VALUE:X3J13-MAR-93}