(def a (seq [ 12 23 32 123 ]))
(def b (seq[ 5 293 400 ]))
(def c (seq[ 1 2 4 7 8 ]))
(def d (seq[ 10 11 24 500]))
(def e (seq[]))
(def k [a b c d e])
(filter #(false? (nil? (first %1))) k)