(keys map)
Returns a sequence of the map's keys, in the same order as (seq map).
(keys {:keys :and, :some :values})
;;=> (:keys :some)
(keys {})
;;=> nil
(keys nil)
;;=> nil
;; although doc says it only takes a map, this still works:
(keys (filter (fn [[_ v]] (-> v :t)) {:a {:t true} :b {:t false} :c {:t true}}))
;;=> (:a :c)