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.
intros.
unfold Projp.
split.
apply l8_14_2_1a in H.
apply perp_not_eq_1 in H.
assumption.
left.
split.
apply perp_in_col in H.
spliter.
assumption.
apply l8_14_2_1a in H.
assumption.
Qed.

Lemma proj_distinct : forall P P' A B, Projp P P' A B -> P' <> A \/ P' <> B.