premise: A park contains at most five of seven kinds of trees—firs, laurels, maples, oaks, pines, spruces, and yews—consistent with the following conditions: If maples are in the park, yews are not. If firs are in the park, pines are not. If yews are not in the park, then either laurels or oaks, but not both, are in the park. If it is not the case that the park contains both laurels and oaks, then it contains firs and spruces. If pines are in the park, then which one of the following must be true?
hypothesis: Neither firs nor maples are in the park.