(defun colinear-p (p1 p2 p3 p4 fuzz / a1 a2)
  (setq a1 (angle p1 p2) a2 (angle p3 p4))
  (and (or (equal a1 a2 fuzz) (equal a1 (+ a2 PI) fuzz));at least parallel
       (equal 0.0 (distance p3 (inters p1 p2 p3 (polar p3 (+ a2 (/ PI 2)) 1.0) nil)) fuzz)
  )
);colinear

(defun C:COL ( / )
  (setq e1 (car(entsel "Select 1st line: "))
        e2 (car (entsel "Select 2nd line: "))
        p1 (cdr (assoc 10 (entget e1)))
        p2 (cdr (assoc 11 (entget e1)))
        p3 (cdr (assoc 10 (entget e2)))
        p4 (cdr (assoc 11 (entget e2)))
        fuzz 0.000000001
  )
  (colinear-p p1 p2 p3 p4 fuzz)  
)