Throws me off a bit early on, you go directly from dog being an actual dog to dog being an arbitrary variable name. At this point I think of dog as “some x such that x is a dog”, so {dog} and {cat} are different because one has an x that is a dog and another has a y that is a cat which is not a dog.
Throws me off a bit early on, you go directly from dog being an actual dog to dog being an arbitrary variable name. At this point I think of dog as “some x such that x is a dog”, so {dog} and {cat} are different because one has an x that is a dog and another has a y that is a cat which is not a dog.