Section Cosinus2.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
Global Instance lcos_morphism :
Proper (EqL ==> EqL ==> eq ==> iff) Lcos.

Lemma l13_7 : forall a b l la lb lab lba, Lcos la l a -> Lcos lb l b ->
Lcos lab la b -> Lcos lba lb a -> EqL lab lba.