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

> Just one more question, for clarification. Are you using the `lambda` form in BSL? I ask because several examples in this thread have been using `lambda`, but I 
> don't think that lambda expressions are actually valid in either of the beginning student languages, though I would expect you to receive an error about lambda 
> being undefined in that situation.

Turns out I'm wrong, I'd never tried to use lambda in BSL before, but it should work.

Dan