Sovereign immunity — Foreign State and State-owned corporations — Commercial activity — Meaning and scope — Whether relating to specific act of which complaint made or normal activity of defendant — Procedure — Removal of action against foreign State to Federal court — Whether involving removal of actions against co-defendants — Act of State doctrine — Refusal of entry by immigration officials — Deportation — Whether acts of State — Whether doctrine precludes judicial inquiry into commercial consequences flowing from those acts — The law of the United States