split0 (IntMap (WordMap m@(NonEmpty min _ Tip)))
    | w2i min < 0 = (m, Empty)
    | otherwise = (Empty, m)
split0 (IntMap (WordMap m@(NonEmpty min _ Tip)))
    | w2i min < 0 = (m, Empty)
    | otherwise = (Empty, m)
split0 (IntMap (WordMap m@(NonEmpty min _ Tip)))
    | w2i min < 0 = (m, Empty)
    | otherwise = (Empty, m)