Learning Functional Programming in Go

Invalid categories

Here, we have two valid categories. The first one is of a car. The objects include the car itself, the car's model name, and the car's age. We show two identity morphisms. One arrow goes from a car to itself (upgrade a car and it's another car). The other arrow goes from the integer object to itself (the "++" operator means add one to the current value). We left off the arrow from the model name to itself, but it exists (a name is a name):=

Why is this invalid? It looks like it composes, but does it really?

The next example should be a bit more obvious. (Funny, but obviously not a category.)

There's a link from the Favorite's ...