premise: Each of exactly seven professors—Powell, Shihab, Taylor, Vaughan, Wood, Young, and Zabel—gives exactly one guest lecture in the literary theory course. The lectures are ordered from first through seventh, and their order must conform to the following: Powell lectures before Wood. Taylor lectures before Shihab. Vaughan lectures before Zabel. Shihab is no later than third. Young is not seventh. Powell lectures first if, but only if, Young lectures before Vaughan. If Zabel lectures fourth, then which one of the following could be true?
hypothesis: Young lectures sixth.