The well ordering property can be used to show that there is a unique greatest common divisor of two positive integers. Let a and b be positive integers, and let S be the set of positive integers of the form as bt, where s and t are integers. a) Show that S is nonempty b) Use the well ordering property to show that S has a smallest element c. c) Show that if d is a common divisor of a and b, then d is a divisor of c. d) Show that c | a and c | b [Hint: First, assume that c does not divide a. Then a