Definition ParaP := fun A B C D =>
forall l m, IncidL A l -> IncidL B l -> IncidL C m -> IncidL D m -> Para l m.

Lemma EqL_dec : forall l m, EqL l m \/ ~EqL l m.
Definition is_line A B l := A <> B /\ IncidL A l /\ IncidL B l.