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;; JACAL: Symbolic Mathematics System. -*-scheme-*-
;; Copyright 1989, 1990, 1991, 1992, 1993, 1995 Aubrey Jaffer.
;;
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2 of the License, or (at
;; your option) any later version.
;;
;; This program is distributed in the hope that it will be useful, but
;; WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with this program; if not, write to the Free Software
;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
(require 'common-list-functions)
;;; delete all occurrences of a from b non-destructively
(define (del a b acc)
(cond ((null? a) b)
((null? b) acc)
((equal? a (car b))
(del a (cdr b) acc))
(else (del a (cdr b) (append acc (list (car b)))))))
(define (factorial n)
(letrec ((factorial1
(lambda (i acc)
(if (< i 2) acc (factorial1 (+ -1 i) (* acc i))))))
(factorial1 n 1)))
(define (cart-prod choices)
(if (null? choices) '(())
(let* ((choice (car choices)))
(apply append
(map (lambda (tuple)
(map (lambda (elt)
(cons elt tuple))
choice))
(cart-prod (cdr choices)))))))
;;;; From Mike Thomas:
;;; Return all the unique subsets of size n obtainable from the list l
(define (combinations l n)
(letrec ((combs1
(lambda (l1 l2 n acc)
(let* ((l1l (length l1))
(l2l (length l2))
(sumls (+ l1l l2l)))
(cond
((< sumls n) acc)
((= sumls n) (append acc (list (append l1 l2))))
((= l1l (+ -1 n))
(append acc (map (lambda (x) (append l1 (list x))) l2)))
(else (apply append
(map (lambda (x y)
(combs1 (append l1 (list x)) y n acc))
l2 (make-ends (cdr l2) '()))))))))
(make-ends
(lambda (l acc)
(if (null? l)
(append acc '(()))
(make-ends (cdr l) (append acc (list l)))))))
(combs1 '() l n '())))
;;; (UNIQUES L) removes any element in each member of a list of lists
;;; that is present in any other member of the list of lists,
;;; preserving order.
;;; (BUILD-UNIQUE-ITEMS L1 L2) builds a list of the members of l1
;;; which are not members of each list in the list l2.
(define (uniques l)
(letrec ((unis
(lambda (a b c)
(cond ((null? b) c)
(else
(unis (cons a (list (car b)))
(cdr b)
(let ((l1 (car b))
(l2 (append a (cdr b))))
(for-each
(lambda (x)
(if (some (lambda (sl) (member x sl)) l2)
(set! l1 (del x l1 '())))) l1)
(append
c (list l1)))))))))
(unis '() l '())))
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