A 2-dimensional space-time line element represented with tortoise coordinate around an event horizon, in every non-static spherically symmetric or plane-symmetric space-time, is explicitly conformal to the 2- dimensional Minkowski line element.

• 在动态球对称或平面对称时空中,用乌龟坐标表示的二维时空线元,在视界附近一定显式共形于二维明氏时空线元。