Given the relatively surrealist reasoning to which the CJEU is forced by the naivety of the Consiglio di Stato's referral, it is worth reproducing it almost in full:
53 [...] the referring court asks, in essence, whether it may decide that a ruling which it has made which has led to a situation which is incompatible with the EU legislation on public works contracts is ineffective.
54 [...] in the absence of EU legislation in this area, the rules implementing the principle of res judicata are a matter for the national legal order, in accordance with the principle of the procedural autonomy of the Member States, but must be consistent with the principles of equivalence and effectiveness (see, to that effect, the judgment in Fallimento Olimpiclub, C‑2/08, EU:C:2009:506, paragraph 24 and the case-law cited).
55 In its request for a preliminary ruling, the referring court indicates that, according to its case-law, it may, under certain conditions, supplement the original operative part of one of its judgments by implementation decisions, that possibility giving rise to what it terms ‘progressively formed res judicata’.
56 If — and it is for the referring court to ascertain whether this is the case — the conditions for applying that procedure are met in respect of the decision in Judgment No 4267/2007, a decision which is mentioned in paragraph 15 of this judgment and which — according to the order for reference — alone has the force of res judicata in the present case, it is for that court, having regard to the principle of equivalence, to make use of that procedure, favouring, from among ‘the numerous different possibilities of implementation’ which it states may be used in respect of that decision, the solution which, in accordance with the principle of effectiveness, ensures compliance with the EU legislation on public works contracts.
58 On the other hand, if the referring court is led to the view that the correct application of that legislation conflicts, having regard to the applicable domestic rules of procedure, with its Judgment No 4267/2007 or with its decisions of 15 April and 3 December 2010 implementing that judgment, attention should be drawn to the importance, both in the legal order of the European Union and in national legal systems, of the principle of res judicata. In order to ensure both stability of the law and legal relations and the sound administration of justice, it is important that judicial decisions which have become definitive after all rights of appeal have been exhausted or after expiry of the time-limits provided for in that connection can no longer be called into question (judgments in Kapferer, C‑234/04, EU:C:2006:178, paragraph 20; Commission v Luxembourg, C‑526/08, EU:C:2010:379, paragraph 26; and ThyssenKrupp Nirosta v Commission, C‑352/09 P, EU:C:2011:191, paragraph 123).
59 Therefore, EU law does not require a national court to disapply domestic rules of procedure conferring finality on a judgment, even if to do so would make it possible to remedy a domestic situation which is incompatible with EU law (see, to that effect, the judgments in Eco Swiss, C‑126/97, EU:C:1999:269, paragraphs 46 and 47; Kapferer, EU:C:2006:178, paragraphs 20 and 21; Fallimento Olimpiclub, EU:C:2009:506, paragraphs 22 and 23; Asturcom Telecomunicaciones, C‑40/08, EU:C:2009:615, paragraphs 35 to 37; and Commission v Slovakia, C‑507/08, EU:C:2010:802, paragraphs 59 and 60).
60 Accordingly, EU law does not require a judicial body automatically to go back on a judgment having the authority of res judicata in order to take into account the interpretation of a relevant provision of EU law adopted by the Court after delivery of that judgment.
61 That analysis cannot be undermined by the judgment in Lucchini (C‑199/05, EU:C:2007:434), cited by the referring court: it was in a highly specific situation, in which the matters at issue were principles governing the division of powers between the Member States and the European Union in the area of State aid, that the Court found, in essence, that EU law precludes the application of a provision of national law, such as Article 2909 of the Italian Civil Code, which seeks to lay down the principle of res judicata, in so far as the application of that provision would prevent the recovery of State aid which was granted in breach of EU law and which has been found to be incompatible with the common market in a decision of the European Commission which has become final (see, to that effect, the judgment in Fallimento Olimpiclub, EU:C:2009:506, paragraph 25). However, issues of that nature, relating to the division of powers, do not arise in the present case.
62 That said, if the applicable domestic rules of procedure provide the possibility, under certain conditions, for a national court to go back on a decision having the authority of res judicata in order to render the situation compatible with national law, that possibility must prevail if those conditions are met, in accordance with the principles of equivalence and effectiveness, so that the situation at issue in the main proceedings is brought back into line with the EU legislation on public works contracts.
63 In that regard, it should be emphasised that that legislation contains fundamental rules of EU law in that it is intended to ensure the application of the principles of equal treatment of tenderers and of transparency in order to open up undistorted competition in all the Member States (see, to that effect, the judgments in Commission v Portugal, C‑70/06, EU:C:2008:3, paragraph 40; Michaniki, C‑213/07, EU:C:2008:731, paragraph 55; Commission v Cyprus, C‑251/09, EU:C:2011:84, paragraphs 37 to 39; and Manova, C‑336/12, EU:C:2013:647, paragraph 28).
64 In the light of the foregoing, the answer to the second question is that, to the extent that it is authorised to do so by the applicable domestic rules of procedure, a national court — such as the referring court — which has given a ruling at last instance, without a reference having first been made to the Court of Justice under Article 267 TFEU, that has led to a situation which is incompatible with the EU legislation on public works contracts must either supplement or go back on that definitive ruling so as to take into account any interpretation of that legislation provided by the Court subsequently (C-213/13 at paras 53-64, emphasis added).