(** First case of congruence of triangles *)

Lemma th12: forall A B C A' B' C',
~ ColH A B C ->
~ ColH A' B' C' ->
CongH A B A' B' ->
CongH A C A' C' ->
CongaH B A C B' A' C' ->
CongaH A B C A' B' C' /\ CongaH A C B A' C' B' /\ CongH B C B' C'.