def [power-set sets] [
    if (empty? sets) [return (list sets)]
    return (join-lists
                (map-apply push
                           (first sets)
                           (power-set (rest sets)))
                (power-set (rest sets)))
]

(? (power-set []))
; [[]]

(? (power-set [[]]))
; [[[]] []]

(? (power-set [1 2 3]))
; [[1 2 3] [1 2] [1 3] [1] [2 3] [2] [3] []]