"""
A TreeList is either None or a Python list with 3 elements
  --- element 0 is a value
  --- element 1 is either a TreeList
  --- element 2 is either a TreeList
"""

def preorder(tl: 'TreeList') -> list:
    """
    Return list of values in tl in preorder

    >>> preorder([5, [4, None, None], [3, [2, None, None], [1, None, None]]])
    [5, 4, 3, 2, 1]
    """
    return [] if tl is None else ([tl[0]] + preorder(tl[1]) + preorder(tl[2]))


def inorder(tl: 'TreeList') -> list:
    """
    Return a list of values of tl inorder

    >>> inorder([5, [4, None, None], [3, [2, None, None], [1, None, None]]])
    [4, 5, 2, 3, 1]
    """
    return [] if tl is None else inorder(tl[1]) + [tl[0]] + inorder(tl[2])

def postorder(tl: 'TreeList') -> list:
    """
    Return list of values in tl in postorder

    >>> postorder([5, [4, None, None], [3, [2, None, None], [1, None, None]]])
    [4, 2, 1, 3, 5]
    """
    return [] if tl is None else postorder(tl[1]) + postorder(tl[2]) + [tl[0]]

if __name__ == '__main__':
    import doctest
    doctest.testmod()