I want to know the answer to the following question:
What 24-hour rapid transit system is outside the United States?
All the background I'm provided with is that "Like the New York City Subway, the PATH operates 24 hours a day; meaning three of the six rapid transit systems in the world which operate on 24-hour schedules are wholly or partly in New York (the others are a portion of the Chicago 'L', the PATCO Speedline serving Philadelphia, and the Copenhagen Metro).". Is that enough to answer the question?
Answer: yes