coordinate in list not found

I have a a couple of connected lines in Autocad representing a pipe network. I have a simple lisp routine that parses through all lines and writes in a list all intersections like that

(defun nodes (/ s ent i p a b w k)    ;  creates text labeling on each intersection

 (setq s (ssget "X" '((0 . "LINE"))))
  
 (setq pl nil)
 (repeat (setq i (sslength s))
(setq ent (entget (ssname s (setq i (1- i)))))
       (setq p (cdr (assoc 10 ent)))
(if (not (member p pl))
	(progn
		(setq k 0)
		(foreach w pl
			(if (not (equal w p 0.001))
				(setq k (1+ k))
			)
		)
		(if (= k (length pl))
			(setq pl (append pl (list p)))
		)
	)
)
				
       (setq p (cdr (assoc 11 ent)))
(if (not (member p pl))
	(progn
		(setq k 0)
		(foreach w pl
			(if (not (equal w p 0.001))
				(setq k (1+ k))
			)
		)
		(if (= k (length pl))
			(setq pl (append pl (list p)))
		)
	)
)   
 )

  (princ)
)

Using this list I want to number these nodes for the lines connected like that

So parsing through each line I have:

(setq pt10 (assoc 10 lineprop))
(setq pt11 (assoc 11 lineprop))

(setq node1 (itoa (1+ (vl-position (cdr pt10) pl))))
(setq node2 (itoa (1+ (vl-position (cdr pt11) pl))))

Here comes my problem. For some reason a point (coordinate) in the pl list is not recognized and gives error that it can not find the (cdr ptxx) in the pl list although apparently it is the same.

I tried to type manually also

!pl

returns: ((0.0 0.0 0.09) (5.0 0.0 0.0) ... (3.0 4.0 5.0) ... (7.0 6.0 6.0) (10.0 6.0 6.0))

(member '(3.0 4.0 5.0) pl)

returns: nil

I understand that the (3.0 4.0 5.0) is not 100% identical with the point in the list. But how can I correct this problem?

Any help would be appreciated.

You need to check with every list of coordinates of the list with a fuzz factor .

eg.

(setq o    (car (entsel "\n Select line :"))
     pt10 (assoc 11 (entget o))
     )

(setq i 0)

(vl-position
 nil
 (mapcar '(lambda (q)
            (if (not (equal (cdr pt10) q 1e-)
              (setq i (1+ i))))
         pl)
 )

Where the variable " i " represents the location of that list of coordinate in the list pl since you are looking for that ,otherwise remove it if you don't want it .

Thanks for your help. That was quite a treat!

Thanks for your help. That was quite a treat!

Cool , you are welcome .