def append(list1, list2):
    result = []
    for item in list1 :
        result = result + [item]
    for item in list2 :
        result = result + [item]
    return result
def concat(lists):
    result = []
    for item in lists
        result = append(result, item)
    return result
def filter(function, list):
    res = []
    if function(item) :
        res = res + item
    return res