from typing import Sequence
from functools import reduce


def list_sum(l:Sequence[list]) -> list:
    """ finished, checked,

    Parameters
    ----------
    l: sequence of list,
        the sequence of lists to obtain the summation

    Returns
    -------
    l_sum: list,
        sum of `l`,
        i.e. if l = [list1, list2, ...], then l_sum = list1 + list2 + ...
    """
    l_sum = reduce(lambda a,b: a+b, l, [])
    return l_sum