International organization — European Coal and Steel Community — Decisions of High Authority — Whether letter can constitute a decision — Criteria — Scope of Treaty establishing Community — Type of enterprise and substance covered — Definition of “steel” — Meaning of “production” in field of coal or steel — Whether pig-iron used in manufacture of product outside Treaty is covered by Treaty — Levy on scrap imposed by High Authority — Whether discriminatory — Meaning of discrimination — Violation of Treaty, Article 5 — Whether imposition of levy disruptive of conditions of competition — Evidence required to prove charge of disruption — Whether levy a special charge prohibited by Treaty.