[racket] TLS "atom?" definition for Scheme does not work in DrRacket

> That's how I found the problem, although I had to chase it down off the
> bottom of the pane.

If the arrow goes off-screen, you can right-click the identifier and select “Jump to Binding Occurrence” to automatically scroll to where the identifier is bound. You can also select “Tack/Untack Arrows” to make the arrows persist even after you move the cursor off the identifier.

Definitely a helpful feature overall.