premise: A train makes five trips around a loop through five stations—P, Q, R, S, and T, in that order—stopping at exactly three of the stations on each trip. The train must conform to the following conditions: The train stops at any given station on exactly three trips, but not on three consecutive trips. The train stops at any given station at least once in any two consecutive trips. If the train is to stop at Q, R, and T on the first trip and at Q, R, and S on the fourth trip, then it could be true that the train
hypothesis: stops at T on the second trip