(defun c:NextLayout ()
  (setvar "ctab" 
    (nth (rem (1+ (vl-position (getvar "ctab") (layoutlist)))
              (length (layoutlist)))
         (layoutlist))
  )
)

(defun c:PreviousLayout ()
  (setvar "ctab" 
    (nth (rem (+ (length (layoutlist)) -1 
                 (vl-position (getvar "ctab") (layoutlist)))
              (length (layoutlist)))
         (layoutlist))
  )
)