Hint Resolve thm7_1.

(* Specifications: *)
Theorem thm7_3 :
forall (l m : Line) (a : Point),
Incident a l -> Incident a m -> Par l m -> EqLn l m.
Theorem thm7_4 :
forall (l m n : Line) (a : Point),
Apart a l -> Incident a m -> Incident a n -> Par n l -> Par m l -> EqLn m n.
Theorem DiLn_qimp_con :
forall l m : Line,
DiLn l m -> ex (fun b : Point => Incident b l /\ Incident b m) -> ConLn l m.
Theorem strict_parallel :
forall (a : Point) (l : Line), Apart a l -> DiLn l (par l a).