二维射影变换中不变直线上至少有一不变点的另证

Another Method to Prove That the Plane Projective Transformation Has at Least One Fixed Point on an Invariant Line

针对平面射影变换中的对偶命题"每一不变直线上至少有一不变点,每一不变点处至少有一条不变直线",给出了两种新的比较简洁的证明方法,并对此命题的真实涵义给予澄清.

Two clear and simple methods were used to prove the dual propositions of plane projective transformation that ＂there is at least＇ one fixed point on an invariant line and an invariant line through a fixed point meanwhile＂. The true connotation of the dual propositions was clarified too.