def append(list1, list2):
    result = []

    for element in list1:
        result.append(element)
    for element in list2:
        result.append(element)
    return result


def concat(lists):
    result = []

    for current_list in lists:
        for element in current_list:
            result.append(element)
    return result


def filter(function, seq):
    result = []

    for element in seq:
        if function(element):
            result.append(element)
    return result


def lenght(seq):
    count = 0

    for element in seq:
        count += 1
    return count


def map(function, seq):
    result = []

    for element in seq:
        result.append(function(element))
    return result