not (ANSI and GNU Common Lisp Document)

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#### 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.