Section Rhombus_Existence_Unicity.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma PlgEquivDef: forall A B C D, (A <> C \/ B <> D) -> ((exists M,
OnCircle C M A /\ OnCircle D M B /\ Bet C M A /\ Bet D M B) <-> Plg A B C D).