(* C5 : For any three angles ^A, ^B, ^C, if ^A = ^Bâ and ^A = ^C, then ^B = ^C. Every angle is congruent to itself. *)

Lemma C5b : forall A B C D E F G H J : Point,
Angle B A C = Angle E D F ->
Angle B A C = Angle H G J ->
Angle E D F = Angle H G J.