def append(list1, list2):
    pusti = []
    for gns in list1:
        pusti.append(gns)
    for exc in list2:
        pusti.append(exc)
    return pusti

def concat(lists):
    pusti = []
    for gns in lists:
        pusti.extend(gns)
    return pusti

def filter(function, list):
    pusti = []
    for gns in list:
        if function(gns):
            pusti.append(gns)
    return pusti

def length(list):
    pocatok = 0
    for gns in list:
        pocatok = pocatok + 1
    return pocatok

def map(function, list):
    pusti = []
    for gns in list:
        pusti.append(function(gns))
    return pusti

def foldl(function, list, initial):
    accumulator = initial
    for gns in list:
        accumulator = function(accumulator, gns)
    return accumulator

def foldr(function, list, initial):
    acc = initial
    for gns in list[::-1]:
        acc = function(acc, gns)
    return acc

def reverse(list):
    return list[::-1]