Fixnum operators

### Fixnum operators

These `fixnum` declared-numeric operators are defined in the `:gbbopen-tools` module:

 Operator Operation Example `&` `the fixnum` `(& x)` `+&` `+` `(+& x y z)` `-&` `-` `(-& x y z)` `1+&` `1+` `(1+& x)` `1-&` `1-` `(1-& x)` `*&` `*` `(*& x y z)` `/&` `/` `(/& x y z)` `=&` `=` `(=& x y z)` `/=&` `/=` `(/=& x y z)` `<&` `<` `(<& x y z)` `<=&` `<=` `(<=& x y z)` `>&` `>` `(>& x y z)` `>=&` `>=` `(>=& x y z)` `abs&` `abs` `(abs& x)` `bounded-value&` `bounded-value` `(bounded-value& x y z)` `ceiling&` `ceiling` `(ceiling& x divisor)` `decf&` `decf` `(decf& x delta)` `decf-&after` `decf-after` `(decf&-after x delta)` `decf/delete&-acons` `decf/delete-acons` `(decf/delete&-acons` `x delta alist)` `evenp&` `evenp` `(evenp& x)` `fceiling&` `fceiling` `(fceiling& x divisor)` `floor&` `floor` `(floor& x divisor)` `ffloor&` `ffloor` `(ffloor& x divisor)` `fround&` `fround` `(fround& x divisor)` `ftruncate&` `ftruncate` `(ftruncate& x divisor)` `incf&` `incf` `(incf& x delta)` `incf&-after` `incf-after` `(incf&-after x delta)` `max&` `max` `(max& x y z)` `min&` `min` `(min& x y z)` `minusp&` `minusp` `(minusp& x)` `mod&` `mod` `(mod& x divisor)` `oddp&` `oddp` `(oddp& x)` `plusp&` `plusp` `(plusp& x)` `pushnew/incf&-acons` `pushnew/incf-acons` `(pushnew/incf&-acons` `'x delta alist)` `round&` `round` `(round& x divisor)` `truncate&` `truncate` `(truncate& x divisor)` `zerop&` `zerop` `(zerop& x)`

The one-argument function coerce& provides convenient `fixnum` coercion:

```  (setf x (coerce& x))
```
Although `(coerce x 'fixnum)` is not permitted in Common Lisp, `(coerce& x)` is equivalent to `(truncate x)` when the remainder is zero and the returned quotient is a `fixnum`. Otherwise, `(coerce& x)` signals an error.

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 Fixnum operators