Let l and m be two lines in ordinary Euclideangeometry intersecting at point O. Let A, B and C be three distinctpoints on l and A', B' and C' three distinct points onm (none of them equal to O). Suppose that AB' is parallelto BA', and AC' is parallel to CA'. Prove, using Pappus'theorem in the Extended Euclidean Plane, that BC' andCB' are parallel.
