Section T7_2.
Context {Tn:Tarski_neutral_dimensionless}.
Context {TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality Tn}.

Lemma l7_21 : forall A B C D P,
~ Col A B C -> B<>D ->
Cong A B C D -> Cong B C D A ->
Col A P C -> Col B P D ->
Midpoint P A C /\ Midpoint P B D.