Global Instance IncidLP_morphisml : Proper(EqL ==> eq ==> iff) IncidLP.Global Instance IncidLP_morphismr : Proper(eq ==> EqP ==> iff) IncidLP.

Lemma soustraction_betH : forall A B C A' B' C' : Point, BetH A B C -> BetH A' B' C' -> CongH A B A' B' -> CongH A C A' C' -> CongH B C B' C'.