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

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

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

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

    def reverse(list):
      pusti = []
    for gns in list:
     pusti.append(gns)
    return pusti[::-1]