State immunity — Attachment and execution — Waiver — Waiver of immunity by foreign State in proceedings against United States corporation — Waiver expressly including agencies of foreign State — Whether assets of State corporation having no connection with underlying legal dispute liable to execution for purposes of enforcing judgment against foreign State — Decision turning on whether corporation alter ego of foreign State — Presumption that State corporation having separate legal personality — Circumstances under which presumption may be rebutted — United States Foreign Sovereign Immunities Act 1976 — The law of the United States