SIGNUM.html -- ACL2 Version 6.3

### SIGNUM

indicator for positive, negative, or zero

    Major Section:  ACL2-BUILT-INS

`(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`.

To see the ACL2 definition of this function, see pf.