Section T8_4.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma col_per2_cases : forall A B C D B',
B <> C -> B' <> C -> C <> D -> Col B C D -> Per A B C -> Per A B' C ->
B = B' \/ ~Col B' C D.