Ltac anga_instance1 a A B C :=
assert(tempo_anga:= anga_const a A B);
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 Angles_5.
Context `{TnEQD:Tarski_neutral_dimensionless_with_decidable_point_equality}.

Lemma eqA_preserves_ang: forall a b, Q_CongA a -> EqA a b -> Q_CongA b.