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

Lemma is_null_anga_dec : forall a, Q_CongA_Acute a -> Q_CongA_Null_Acute a \/ ~ Q_CongA_Null_Acute a.