**MW:** So let’s see. Last time we talked about the functor *B* from the category FinSet to the category BoolAlg of boolean algebras. Liberal infusions of coffee convinced you that *B* is *covariant*; I accidentally suggested it was *contravariant*. I think I’ve come round to your position, but I still have a couple of things I want to say on the matter. If it won’t be too confusing for our readers.

**JB:** Okay. If we’re planning to talk more about the variance, it’s probably *good *to start out by getting the reader a bit confused. I used to always be confused about it myself. Then I finally felt I had it all straightened out. Then you shocked me by arguing that it worked the opposite way. Your argument was very sneaky.