5.3.31 not [Function]

not x ⇒ boolean

Arguments and Values::

x—a generalized boolean (i.e., any object).

boolean—a boolean.

Description::

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

Examples::

 (not nil) ⇒  T
 (not '()) ⇒  T
 (not (integerp 'sss)) ⇒  T
 (not (integerp 1)) ⇒  NIL
 (not 3.7) ⇒  NIL
 (not 'apple) ⇒  NIL

See Also::

null

Notes::

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.