(define (double-up! ls)
  (cond ((null? ls) 'okay)
	((null? (cdr ls)) 'okay)
	(else (begin
		(define temp (car ls))
		(set-car! ls (cdr ls))
		(set-cdr! ls (cdar ls))
		(set-cdr! (car ls) (caar ls))
		(set-car! (car ls) temp)
		(double-up! (cdr ls))))))