Hint Resolve perp_per_1 perp_per_2 perp_col perp_perp_in perp_in_perp : perp.
Section T8_5.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

(* Specifications: *)
Lemma perp_proj : forall A B C D, Perp A B C D -> ~Col A C D -> exists X, Col A B X /\ Perp A X C D.
Lemma l8_24 : forall A B P Q R T,
Perp P A A B ->
Perp Q B A B ->
Col A B T ->
Bet P T Q ->
Bet B R Q ->
Cong A P B R ->
exists X, Midpoint X A B /\ Midpoint X P R.
Lemma col_per2__per : forall A B C P X, A <> B -> Col A B C -> Per A X P -> Per B X P -> Per C X P.
Lemma perp_in_per_1 :
forall A B C D X,
Perp_at X A B C D ->
Per A X C.
Lemma perp_in_per_2 :
forall A B C D X,
Perp_at X A B C D ->
Per A X D.
Lemma perp_in_per_3 :
forall A B C D X,
Perp_at X A B C D ->
Per B X C.
Lemma perp_in_per_4 :
forall A B C D X,
Perp_at X A B C D ->
Per B X D.