Case C-90/09 P: Judgment of the Court (First Chamber) of 20 January 2011 — General Química SA, Repsol Química SA, Repsol YPF SA v European Commission (Appeal — Competition — Agreements, decisions and concerted practices — Rubber chemicals sector — Decision finding an infringement of Article 81 EC — Group of undertakings — Joint and several liability of a parent company for infringements of the competition rules committed by its subsidiaries — Attribution of liability to the parent company at the head of a group)