> What does our theory of databases say about this question? (As opposed to what a psychologist might say about it.)

My understanding is that our theory of databases makes no restriction for a person being their own best friend. In the definition, John wrote:

> Choose any function \$$F(e) : F(x) \to F(y)\$$ for each edge \$$e\$$ in our graph

So functions that map people to themselves are definitely allowed!

A follow up puzzle:

**Puzzle SL 1**
Is there a finitely presented category which constrains people from being their own best friend?