Thornfield Civic Lab uses the following label rules; an otherwise possible overlap is allowed unless these rules block it. Rules: (1) Any case assigned the Topaz Orchard label is assigned the Topaz Iris label as well. (2) A case with the Topaz Yard label cannot also have the Topaz Delta label. (3) Every case with the Topaz Iris label also has the Topaz Yard label. (4) No case assigned Topaz Tide is assigned Topaz Delta. (5) The Topaz Zenith label is allowed only on cases that also have the Topaz Iris label. (6) A case cannot carry the Topaz Echo label unless it also carries the Topaz Orchard label. Which classification is formally impossible on the basis of the rules alone?