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.