(vals map)
Returns a sequence of the map's values, in the same order as (seq map).
(vals {:a "foo", :b "bar"})
;;=> ("foo" "bar")
(vals {})
;;=> nil
(vals nil)
;;=> nil
(defn flatten-a-map [dpdnts-map]
(apply set/union (vals dpdnts-map)))
(flatten-a-map {:e #{:m :f}, :c #{:f}, :b #{:c :f}, :d #{:m :f}, :a #{:c :f}}
;;=> #{:m :c :f}