立体几何课本第11页上,以例题形式给出了一条关于异面直线的判定定理(黑体字):平面内一点与平面外一点的连线,和平面内不经过该点的直线是异面直线。这是立体几何教材开宗明义的第一条定理,然后它登场一次后,几乎不再露面了,在以后的关于异面直线推理中,一般是从原始的定义出发,把这么重要 On page 11 of the 3D geometry textbook, a decision theorem (face in boldface) on a straight line with a different surface is given in the form of an example: the line between a point in the plane and a point outside the plane, and the line in the plane that does not pass through this point is a facet straight line. This is the first theorem of a three-dimensional geometry textbook, and then it is almost no longer visible after it debuts once. In the later line of inference about heterotopia, it is generally based on the original definition and it is so important.