p0{0,1,2,3,4}*.rkt 
  -- the Redex developments that have been typed/shown during the talk.

p05_bonus_arith_expr_many_formats.rkt
  -- a bonus development that demonstrates that we can encode various 
     semantic formats inside Redex (reduction semantic, abstract machine,
     natural semantics, structural operational semantics (SOS)).

p06_lambda_calculus.rkt
  -- a bonus development exemplifying the encoding of a language with
     binders using the example of the untyped lambda calculus.

To play with the files, simply open them in DrRacket. It might be the
best to paste the definitions (define ..., define-language etc) into
the upper buffer, and the queries into the lower buffer (the REPL). 
Alternatively, you can install an Emacs mode ('geiser' worked
for me) for Racket and use C-x C-e on each of the S-expressions in
turn.
