This is not a list? Also you probably shouldn’t name your entites neither first
nor rest
.
Assuming you have a vector of the stuff you want to concatenate on the first vector, you could do:
(def some-things [{:a 1} {:a 2}])
(def more-things [[{:a 3} {:a 4}] [{:a 5} {:a 6}]])
(concat some-things (flatten more-things))
=> ({:a 1} {:a 2} {:a 3} {:a 4} {:a 5} {:a 6})
But someone will tell us that whenever you use flatten
you have done something wrong.