ALPHORDER.html -- ACL2 Version 6.3

### ALPHORDER

total order on atoms

    Major Section:  ACL2-BUILT-INS

`Alphorder` is a non-strict total order, a ``less than or equal,'' on atoms. By ``non-strict total order'' we mean a function that always returns `t` or `nil` and satisfies the following properties.

> o Antisymmetry: `XrY & YrX -> X=Y`

> o Transitivity: `XrY & YrZ -> XrZ`

> o Trichotomy: `XrY v YrX`

Also see lexorder, which extends `alphorder` to all objects.

`(Alphorder x y)` has a guard of `(and (atom x) (atom y))`.

Within a single type: rationals are compared arithmetically, complex rationals are compared lexicographically, characters are compared via their char-codes, and strings and symbols are compared with alphabetic ordering. Across types, rationals come before complexes, complexes come before characters, characters before strings, and strings before symbols. We also allow for ``bad atoms,'' i.e., atoms that are not legal Lisp objects but make sense in the ACL2 logic; these come at the end, after symbols.

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