Axiom
constructed_orthogonal :
forall (l : Line) (a : Point), {l' : Line | Ort l' l /\ Incident a l'}.
Definition ort : Line -> Point -> Line.

Theorem thm8_6 : forall l m n : Line, ConLn l m -> Unort l n \/ Unort m n.
Definition Oblique : Relation Line :=
fun l m : Line => ConLn l m /\ Unort l m.