overlapping sets

;; OVERLAPPING SETS
;; (overlap-sets '((1 2 3) (4 5 3) (6 7 8 9))) -> ((5 4 1 2 3) (6 7 8 9))

(define (overlap-set-with-sets set sets leftover)
  (if (null? sets)
      (cons set leftover)
      (let ([is (lset-intersection = set (car sets))])
  (if (null? is)
	    (overlap-set-with-sets set (cdr sets) (cons (car sets) leftover))
	    (overlap-set-with-sets (lset-union = set (car sets)) (cdr sets) leftover)))))
(define (overlap-sets sets)
  (if (null? sets)
      '()
      (let ([res (overlap-set-with-sets (car sets) (cdr sets) '())])
	(if (equal? (car res) (car sets)) ; didn't find anything
	    (cons (car res) (overlap-sets (cdr res)))
	    (overlap-sets res)))))