Section T8_4.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma Perp_cases :
forall A B C D,
Perp A B C D \/ Perp B A C D \/ Perp A B D C \/ Perp B A D C \/
Perp C D A B \/ Perp C D B A \/ Perp D C A B \/ Perp D C B A ->
Perp A B C D.