premise: On a single day, a realtor will show a client five houses, exactly one house in each of five neighborhoods—Quarry, Riverton, Shelburne, Townsend, and Valencia. Each house will be shown to the client exactly once. The order in which the houses are shown is subject to the following constraints: The house in Riverton must be shown either first or second. The house in Townsend must be shown either first or fifth. The third house shown must be the house in Quarry or the house in Valencia. The house in Quarry cannot be shown either immediately before or immediately after the house in Shelburne. Which one of the following, if substituted for the constraint that the house in Riverton must be shown either first or second, would have the same effect on the order in which the houses are shown?
hypothesis: If the house in Townsend is not shown fifth, then it must be shown immediately before the house in Riverton.