unknown | yes | no has the same cardinality (3) of unknown | boolean as you can replace boolean with yes | no. If you write code that has to handle it, you sti

unknown | yes | no has the same cardinality (3) of unknown | boolean as you can replace boolean with yes | no. If you write code that has to handle it, you still need to consider 3 cases, you can never reduce it to two cases only.