Racket is great, and I'm not trying to pick nits, but it's not a Lisp, it's a Scheme dialect. If you want to learn pure Lisp, I'd recommend Paul Graham's book, On Lisp, which is available online for free.
It is.
"... pure Lisp ..."
There is no such a thing as "pure Lisp". Lisp is not a programming language, it's a family of programming languages that share some common properties.
To put it more clearly, we could represent Lisp and its members hierarchically:
Lisp
Common Lisp
CLISP
SBCL
...
Scheme
Racket
Gambit
Chicken
...
Clojure
...