premise: A store sells shirts only in small, medium, and large sizes, and only in red, yellow, and blue colors. Casey buys exactly three shirts from the store. A shirt type consists of both a size and a color. Casey does not buy two shirts of the same type. Casey does not buy both a small shirt and a large shirt. No small red shirts are available. No large blue shirts are available. If neither large red shirts nor small blue shirts are available, which one of the following must Casey buy?
hypothesis: either a medium red shirt or a medium blue shirt