Case C-116/12: Judgment of the Court (Sixth Chamber) of 12 December 2013 (request for a preliminary ruling from the Diikitiko Protodikio Serron (Greece)) — Ioannis Christodoulou, Nikolaos Christodoulou, Afi N. Christodoulou AE v Elliniko Dimosio (Customs value — Goods exported to a third country — Export refunds — Processing in the exporting country regarded as non-substantial — Re-export of goods to the European Union — Determination of the customs value — Transaction value)