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I am a Clojure beginner, I don't understand the concept of immutable data.
Because the complier allow me to def the 'girl1' more then 1 time below:
(def girl1 "stephanie")
(def girl1 "ann")
(def girl3 "victoria")
(println girl1 girl3))
def creates a var, which is stateful (mutable) box referring to a value. The values here are all strings, which are immutable.