Case T-100/17: Judgment of the General Court of 11. December 2018 — BTB Holding Investments and Duferco Participations Holding v Commission (State aid — Steel industry — Aid granted by Belgium in favour of a number of undertakings in the iron and steel industry — Decision declaring that aid incompatible with the internal market and ordering its recovery — Obligation to state reasons — Concept of State aid — Advantage — Private investor test)