Find duplicates in a sequence using Clojure

DuplicateFinder.clj

(defn extract-names [seq]
  (for [lib seq :let [dot-index (.indexOf lib ".")]]
    (subs lib 0 (- dot-index 2))))


;(println (extract-names ["x-security-1.0.7.jar"  "aksis-1.0.jar" "antlr-2.7.6.jar"]))

(defn dups [seq]
  (for [[id freq] (frequencies seq)                         ;; get the frequencies, destructure
        :when (> freq 1)]                                   ;; this is the filter condition
    id))

(println (dups (extract-names [
                               "asm-3.2.jar"
                               "asm-analysis-3.2.jar"
                               "asm-commons-3.2.jar"
                               "asm-tree-3.2.jar"
                               "asm-util-3.2.jar"
                               "castor-1.2.jar"
                               "cglib-2.2.jar"
                               "cglib-nodep-2.1_3.jar"
                               "commons-pool-1.3.jar"
                               "docx4j-3.0.1.jar"
                               "dom4j-1.6.1.jar"
                               "jsoup-1.7.2.jar"
                               "jsoup-1.7.3.jar"
                               "ognl-2.6.11.jar"
                               "ognl-2.6.9.jar"
                               "sac-1.4.jar"
                               ])))