Suppose that points A,B,C,A', B', C' lie on con- current lines L, M, N as shown in Figure 1.15. (The triangles ABC and A'B'C' are said to be "in perspective from O.") 0 C A B C' A' Figure 1.15: The parallel Desargues configuration OA OC = B' Use the Thales theorem to show that if AB is parallel to A'B' and BC is parallel to B'C', then OA' OC' L N