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;;; -*- Mode: Lisp -*-
;;;
;;; PERMUT: A Package for generating permutations
#-NIL(includef (cond ((status feature ITS) '|libmax;prelud >|)
((status feature Multics) '|prelude|)
((status feature Unix) '|libmax//prelud.l|)
(t (error '|Unknown system -- see MC:LIBMAX;INCLUD >|))))
#-NIL(declare (mapex T))
(defun all_permutations (l)
(if (null l) '(())
(do ((elt (car l))
(permute (all_permutations (cdr l)) (cdr permute))
(ans))
((null permute) ans)
(setq ans
(append (permute_an_elt_through elt (car permute)) ans)))))
(defun permute_an_elt_through (elt l)
(if (null l) (ncons (ncons elt))
(cons (cons elt l)
(mapcar #'(lambda (x) (cons (car l) x))
(permute_an_elt_through elt (cdr l))))))
(defun $permutations (l)
(if ($listp l)
(cons '(MLIST) (mapcar #'(lambda (x) (cons '(MLIST) x))
(all_permutations (cdr l))))
(displa l)
(merror "~&Error, argument not a list---PERMUTATIONS~%")))
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