How does LINQPad reference other classes, e.g. Books in the LINQ in Action samples

If you right click in the code editor in LINQPad and choose Advanced Query Properties, there are two dialogs: Additional References and Additional Namespace Imports.

1) In Additional References, choose Add then click Browse and navigate to your custom assembly.

2) Then, in Additional Namespace Imports, type the namespaces you want to import from that assembly.