cl:union   scheme

(define cl:union
  (letrec ((onion
      (lambda (lst1 lst2)
        (if (null? lst1)
      lst2
      (onion (cdr lst1) (cl:adjoin (car lst1) lst2))))))
    (lambda (lst1 lst2)
      (cond ((null? lst1) lst2)
      ((null? lst2) lst1)
      ((null? (cdr lst1)) (cl:adjoin (car lst1) lst2))
      ((null? (cdr lst2)) (cl:adjoin (car lst2) lst1))
      ((< (length lst2) (length lst1)) (onion (reverse lst2) lst1))
      (else (onion (reverse lst1) lst2))))))
;@