Vector with a single X bit (lsb), upper bits all 0.
Definition: *4vec-1x*
(defconst *4vec-1x* (make-honsed-4vec :upper 1 :lower 0))
Macro: 4vec-1x
(defmacro 4vec-1x nil (cons 'quote (cons *4vec-1x* 'nil)))
