Global Instance lcos_morphism :
 Proper (EqL ==> EqL ==> eq ==> iff) Lcos.

Lemma lcos_eq_lcos3_eq : forall la lb a b c d, Q_CongA_Acute c -> Q_CongA_Acute d -> Eq_Lcos la a lb b -> Eq_Lcos3 la a c d lb b c d.