(* Gabriel Braun April 2013 *)
Require Export GeoCoq.Tarski_dev.Ch13_3_angles.
Ltac anga_instance_o a A B P C :=
assert(tempo_anga:= anga_const_o a A B P);
match goal with
|H: Q_CongA_Acute a |-  _ => assert(tempo_H:= H); apply tempo_anga in tempo_H; ex_elim tempo_H C
end;
clear tempo_anga.
Section Cosinus.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.
(************************************* cos *****************************)

Lemma eql_lcos_null : forall l lp a, Lcos l lp a -> EqL l lp -> Q_CongA_Null_Acute a.