Section T8_4.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma Perp_in_perm :
forall X A B C D,
Perp_at X A B C D ->
Perp_at X A B C D /\ Perp_at X B A C D /\ Perp_at X A B D C /\ Perp_at X B A D C /\
Perp_at X C D A B /\ Perp_at X C D B A /\ Perp_at X D C A B /\ Perp_at X D C B A.