## SIGNUM

indicator for positive, negative, or zero
Major Section: PROGRAMMING

`(Signum x)`

is `0`

if `x`

is `0`

, `-1`

if `x`

is negative,
and is `1`

otherwise.

The guard for `signum`

requires its argument to be rational (real, in
ACL2(r)) number.

`Signum`

is a Common Lisp function. See any Common Lisp
documentation for more information.

From ``Common Lisp the Language'' page 206, we see a definition of
`signum`

in terms of `abs`

. As explained elsewhere
(see abs), the guard for `abs`

requires its argument to be a
rational (real, in ACL2(r)) number; hence, we make the same
restriction for `signum`

.