Clojure: maps as keys

gistfile1.clj

;; After https://gist.github.com/jjconti/054e15b5a9a07ecadf33
user=> (def d {:a 1 :b 2 :c 3})
#'user/d
user=> (:b d)
2
user=> (d :b)
2

;; Can dictionaries be keys in another dictionary? 
;; What if two dictionaries have each other as keys?
user=> (def metadict {d 42})
#'user/metadict
user=> (assoc d metadict 99)
{{{:c 3, :b 2, :a 1} 42} 99, :c 3, :b 2, :a 1}
user=> (metadict d)
42
user=> (d metadict)
nil
user=> d
{:c 3, :b 2, :a 1}
user=> (def d (assoc d metadict 99))
#'user/d
user=> metadict
{{:c 3, :b 2, :a 1} 42}
user=> d
{{{:c 3, :b 2, :a 1} 42} 99, :c 3, :b 2, :a 1}
user=> (d metadict)
99