(let [hello (fn
                  ([] "Hello World!")
                  ([a] (str "Hello, you silly " a "."))
                  ([a & more] (str "Hello to this group: "
                                   (apply str
                                          (interpose ", " (concat (list a) more)))
                                   "!")))]
      (= __
         (hello "Peter" "Paul" "Mary")))