Thank you, I tried that and it worked.

Hopefully that can be added to the instructions in the book so that people like me who are learning Clojure as they are learning how to make web apps using it can be less confused.

Dmitri Sotnikov @dmitri and Scot Brown @svmbrown

Working through this now and encountered same issue, so thanks for this thread!

In addition, I found on p. 9

A common beginner error that you may encounter is forgetting to start the
database connection. If you do get this error, don’t worry—just run (start) and try again. In fact, any error that mentions mount.core.DerefableState is probably due to forgetting to run (start).

But I agree. There should be an additional sentence telling the reader to not only start the REPL (which it does) but to also ‘(start)’ especially since we are a long way from p. 9!