;;; Paths from one node to another
;;; uses adjacency-list form

(defun path (g a b)
  (path-using g a b (all-nodes g))
  )

(defun path-using (g a b available)
  (if (equal a b)
      (list (list a))
    (let ((path-list nil))
      (dolist (n (adj-list g a) (addto a path-list))
	(if (member n available)
	    (setf path-list 
		  (append (path-using g n b (remove a available)) path-list)
		  )
	  )
	)
      )
    )
  )

(defun adj-list (g a)
  (second (assoc a g))
  )

(defun addto (a paths)
  (mapcar #'(lambda (x) (cons a x)) paths)
  )

(defun all-nodes (g)
  (mapcar #'car g)
  )