@Keith [comment38](https://forum.azimuthproject.org/discussion/comment/19829/#Comment_19829), the collection of objects \$$\mathrm{Ob}(\mathbf{Set})\$$ in the category \$$\mathbf{Set}\$$ is not a set, it is a [class](https://en.wikipedia.org/wiki/Class_(set_theory)). This means \$$\mathbf{Set}\$$ is a [**large category**](https://en.wikipedia.org/wiki/Category_(mathematics)#Small_and_large_categories), echoing Anindya's [comment#41](https://forum.azimuthproject.org/discussion/comment/19833/#Comment_19833). This is a way to resolve Cantor's/Russell's Paradox. I think John intentionally left it out so that we won't get distracted by the technicality.