(cat rf)
A transducer which concatenates the contents of each input, which must be a collection, into the reduction.
;; cat is handy for untangling nested collections when using transducers
(into [] (comp cat cat (map inc)) [[[1] [2]] [[3] [4]]])
;; => [2 3 4 5]
;; Remove the need of (mapcat identity coll) idiom:
(def rota (sequence cat (repeat ["tom" "nick" "jane"])))
(nth rota 7) ; who's up next week?
;; nick