Transitive Closure of a Binary Relation

gistfile1.clj

(defn transitive-closure [rel]
  (let [roots (into {} (for [[k v] (group-by first rel)] [k (mapv second v)]))
        children (fn children [rels e] 
                   (let [cs (get rels e [])]
                     (cons e (mapcat #(children rels %) cs))))]
    (set (mapcat #(map vector (repeat %) (rest (children roots %))) (keys roots)))))

(transitive-closure #{[8 4] [9 3] [4 2] [27 9]})
(transitive-closure #{["cat" "man"] ["man" "snake"] ["spider" "cat"]})