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Function NOT


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

Side Effects: None.

Affected By: None.

Exceptional Situations: None.

See Also:



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.

The following X3J13 cleanup issue, not part of the specification, applies to this section:

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