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not (Function)

Syntax:
— 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 (Function)

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.