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not (Function)

— Function: not x boolean
Arguments and Values:

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
See Also:

null (Function)


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.