Challenge of an arbitral award for violation of rules of law is always permitted when such violation concerns the resolution of a preliminary question relating to matters excluded from arbitral jurisdiction, regardless of whether the preliminary question does not directly constitute the subject matter of the arbitration agreement.
In challenges for nullity of an arbitral award, grounds of appeal that merely contest technical evaluations and findings of fact made by the arbitrators, without affecting the ratio decidendi of the impugned decision, are inadmissible for lack of specificity of the challenge.