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Opinion of Advocate General Wathelet delivered on 15 October 2015 Opinion of Advocate General Wathelet delivered on 15 October 2015.#Puligienica Facility Esco SpA (PFE) v Airgest SpA.#Request for a preliminary ruling from the Consiglio di Giustizia amministrativa per la Regione siciliana.#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.#Case C-689/13.