Section Projections.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.
intros.
unfold Proj in H0.
spliter.
induction H4; tauto.
Qed.
intros.
unfold Proj in *.
spliter.
repeat split; Col.
Qed.
intros.
unfold EqV in H.
induction H.
apply plg_cong.
apply plg_permut.
apply plg_comm2.
assumption.
spliter.
subst B.
subst D.
Cong.
Qed.

Lemma perp_projp : forall P P' A B, Perp_at P' A B P P' -> Projp P P' A B.