This definition is valid for arbitrary complex order "s" and for all complex arguments "z" with |"z"| < 1; it can be extended to |"z"| ≥ 1 by the process of analytic continuation. The special case "s" = 1 involves the ordinary natural logarithm, Li1("z") = −ln(1−"z"), while the special cases "s" = 2 and "s" = 3 are called the dilogarithm (also referred to as Spence's function) and trilogarithm respectively. The name of the function comes from the fact that it may also be defined as the repeated integral of itself: