This `concat` is causing tests to fail, but using `into` fixes it. I'll submit a patch shortly.

```clojure
(def trends [[827 828 829] [1 2 3] [4 5 6] [7 8 9]])
(def shorts [10 11 12])

(concat (first trends) shorts (take-last 3 trends))
;=> [827 828 829 [10 11 12 ([1 2 3] [4 5 6] [7 8 9])]

(info [(first trends) shorts] (take-last 3 trends))
;=> [[827 828 829] [10 11 12] [1 2 3] [4 5 6] [7 8 9]]
```