Also the Benelux Court of Justice was considered a court within this context, as a court common to several (Netherlands, Belgium, Luxembourg) Member States. Also the Unified Patent Court, as a court common to several Member States is expected to be able to ask prejudicial questions. Article 267 of the Treaty on the Functioning of the European Union (TFEU) establishing the preliminary reference procedure differentiates between the right and the duty of national courts to seek a preliminary ruling. Under the discretionary reference stipulated in Article 267(2) TFEU, a national "court or tribunal" may ask the CJEU to give a preliminary ruling if it considers that a decision on the question is "necessary" to enable it to give a judgment in a particular case. The obligatory reference (duty to refer) is established in two cases: with respect to national courts adjudicating at last instance (Article 267(3) TFEU ) and with respect of all courts faced with a question of the validity of EU law. The obligation of national courts of last instance to refer for a preliminary ruling when a question of the interpretation of EU law arises is subject to certain exceptions. In accordance with the jurisprudence of the Court, a national court is relieved from the duty to refer (i) when EU law questions are not relevant to the decision in the main proceedings, (ii) in a situation before a national court is “materially identical with a question which has already been subject of a preliminary ruling in a similar case” (‘acte éclairé’), or (iii) when the proper interpretation of EU law is “so obvious as to leave no scope for any reasonable doubt” (‘acte clair’). The Court of Justice Decision has the force of res judicata. It is binding not only on the national court on whose initiative the reference for a preliminary ruling was made but also on all of the national courts of the Member States. In the context of a reference for a preliminary ruling concerning validity, if the European instrument is declared invalid all of the instruments adopted based on it are also invalid. It then falls to the competent European institutions to adopt a new instrument to rectify the situation. The European Court of Justice is competent to give rulings regarding the interpretation of treaties to which the European Union is a party, as those treaties are considered to be part of EU law. ECJ is however also competent regarding the application of certain treaties between EU member states, although the procedure may be subject to different procedures.