def METHOD_NAME(self, label=lambda i: i, node=None):
    """
    Return a ascii art representation of the extended Dynkin diagram.
    EXAMPLES::
        sage: print(CartanType(['C',5,1]).ascii_art(label = lambda x: x+2))
        O=>=O---O---O---O=<=O
        2   3   4   5   6   7
        sage: print(CartanType(['C',3,1]).ascii_art())
        O=>=O---O=<=O
        0   1   2   3
        sage: print(CartanType(['C',2,1]).ascii_art())
        O=>=O=<=O
        0   1   2
        sage: print(CartanType(['C',1,1]).ascii_art())
        O<=>O
        0   1
    """
    if node is None:
        node = self._ascii_art_node
    n = self.n
    from .cartan_type import CartanType
    if n == 1:
        return CartanType(["A",1,1]).METHOD_NAME(label, node)
    ret = node(label(0)) + "=>=" + "---".join(node(label(i)) for i in range(1,n))
    ret += "=<=" + node(label(n)) + '\n'
    ret += "".join("{!s:4}".format(label(i)) for i in range(n+1))
    return ret