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

Lemma lcos3_lcos_1_2 : forall lp l a b c, Lcos3 lp l a b c <-> exists la, Lcos la l a /\ Lcos2 lp la b c.