Section Projections.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.
intros.
unfold Proj in H0.
spliter.
induction H4; tauto.
Qed.

Lemma project_idem : forall P P' A B X Y, Proj P P' A B X Y -> Proj P' P' A B X Y.