Let(a,b,c) be a triangle in RP2, and let D be aline not passing through any of a,b,c, so that D intersects〈b,c〉inp,〈c,a〉inq,and〈a,b〉inr. Let La,Lb,Lc be three lines passing through a,b,c,...

Let(a,b,c) be a triangle in RP2, and let D be aline not passing through any of a,b,c, so that D intersects〈b,c〉inp,〈c,a〉inq,and〈a,b〉inr. Let La,Lb,Lc be three lines passing through a,b,c, respectively, and intersecting D in p′,q′,r′.Prove that the reisa unique involution mapping p top′, q to q′, and r to r′iff the lines La,Lb,Lc are concurrent.