4. Again, assume that MM' is the common perpendicular segment between 1 and 1. Let A and B be any points of 1 such that M*A* B, and drop perpendiculars AA' and BB' to 1'. Prove that AA' < BB'. (Hint: use Exercise 3, Chapter 5; see Figure 6.19.) 9 B A M I' M' A' B' B 3. With the same hypothesis as in Exercise 2, prove the converse, that if (D)°<(C), then AC < BD. (Hint: assume the contrary, which involves the two cases ACBD and AC > BD. In each case, derive a contradiction.)