atc-

(def a '())
(def b '(1 2 3))
(def c '(4 5 6))

; I want to produce the following but not adding nils to a. In the example above this doesn't happen because b and c are exhausted at the same time -- I but last in a loop on b and c -- so please imagine each line below is the output of a loop/recur:

; (6 3) (1 2) (4 5)
; (5 2 6 3) (1) (4)
; (4 1 5 2 6 3) nil nil
; (4 1 5 2 6 3)