Definition cut' A B X Y := X <> Y /\ forall l, IncidL X l -> IncidL Y l -> cut l A B.
Global Instance cut_morphism : Proper(EqL ==> eq ==> eq ==> iff) cut.

Lemma cong_preserves_col_stronger : forall A B C A' B' C',
A <> B -> A <> C -> B <> C ->
ColH A B C -> CongH A B A' B' -> CongH B C B' C' -> CongH A C A' C' ->
ColH A' B' C'.