Opinion of Advocate General Tanchev delivered on 22 May 2019.#GRDF SA v Eni Gas & Power France SA and Others.#Request for a preliminary ruling from the Cour de cassation.#Reference for a preliminary ruling — Common rules for the internal market in natural gas — Directive 2009/73/EC — Article 41(11) — Settlement of disputes concerning the obligations imposed on a system operator — Temporal effects of decisions of the dispute settlement authority — Legal certainty — Legitimate expectations.#Case C-236/18.