Case C-689/13: Judgment of the Court (Grand Chamber) of 5 April 2016 (request for a preliminary ruling from the Consiglio di giustizia amministrativa per la Regione siciliana — Italy) — Puligienica Facility Esco SpA (PFE) v Airgest SpA (Reference for a preliminary ruling — Public service contracts — Directive 89/665/EEC — Article 1(1) and (3) — Review procedures — Application for annulment of the decision awarding a public contract by a tenderer whose bid was not successful — Counterclaim brought by the successful tenderer — Rule derived from national case-law under which the counterclaim must be examined first and, if the counterclaim is well founded, the main action must be dismissed as inadmissible without any examination of the merits — Whether compatible with EU law — Article 267 TFEU — Principle of the primacy of EU law — Principle of law stated by decision of the plenary session of the supreme administrative court of a Member State — National legislation which provides that that decision is binding on the chambers of that court — Obligation on the part of the chamber required to adjudicate on a question of EU law to refer that question to the plenary session if it disagrees with the decision of the plenary session — Whether the chamber has a discretion or is under an obligation to request a preliminary ruling from the Court of Justice)