Instance incident_Proper (A:Tpoint) :
Proper (EqL ==>iff) (IncidentL A).

(** There is only one line going through two points. *)
Lemma axiom_line_uniqueness : forall A B l m, A <> B ->
IncidentL A l -> IncidentL B l -> IncidentL A m -> IncidentL B m ->
l =l= m.