Write a function with the following type:
val minmax : (int -> 'a) -> int -> int -> 'a * 'a = <fun>When fed with a function f: int -> int and two integers a,b
such that a<=b, the expression minmax f a b evaluates to a pair
(min,max), where min and max are, respectively,
the minimum and the maximum of f in the range [a,b].