28. In A. M. Fink’s procedure (described in Exercise 27), suppose that a fourth person (Alice) comes along after Bob, Carol, and Ted have already divided the cake among themselves so that each of the three thinks that he or she has a piece of size at least one-third. Mimic what was done in the three-person case to obtain an allocation among the four that is proportional. (Hint: Begin by having Bob, Carol, and Ted divide the pieces they have into a certain number—how many?—of equal parts.)