State immunity — Jurisdictional immunity — Commercial activity exception — Distinction between commercial acts and sovereign acts — Distinction turning on nature rather than purpose of act — Torts exception — Recruitment of staff in United States to work in hospital in Saudi Arabia — Alleged false imprisonment and ill-treatment of member of staff by agents or employees of Saudi Government — Whether falling within commercial activity exception — Exercise of police powers — Whether operation of hospital a commercial activity — Whether action in tort based upon that activity — Whether sufficient connection with the United States — The law of the United States