ABS.html -- ACL2 Version 6.3

### ABS

the absolute value of a real number

    Major Section:  ACL2-BUILT-INS

`(Abs x)` is `-x` if `x` is negative and is `x` otherwise.

The guard for `abs` requires its argument to be a rational (real, in ACL2(r)) number.

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

From ``Common Lisp the Language'' page 205, we must not allow complex `x` as an argument to `abs` in ACL2, because if we did we would have to return a number that might be a floating point number and hence not an ACL2 object.

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