premise: An album contains photographs picturing seven friends: Raimundo, Selma, Ty, Umiko, Wendy, Yakira, Zack. The friends appear either alone or in groups with one another, in accordance with the following: Wendy appears in every photograph that Selma appears in. Selma appears in every photograph that Umiko appears in. Raimundo appears in every photograph that Yakira does not appear in. Neither Ty nor Raimundo appears in any photograph that Wendy appears in. If Umiko and Zack appear together in a photograph, then exactly how many of the other friends must also appear in that photograph?
hypothesis: zero