Section T10.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
Goal forall A B C D, ~ Coplanar D C B A -> ~ Coplanar A B C D.

Lemma midpoint_preserves_per : forall A B C A1 B1 C1 M,
Per A B C ->
Midpoint M A A1 ->
Midpoint M B B1 ->
Midpoint M C C1 ->
Per A1 B1 C1.