(Ex. 10.7 of Sethi) Suppose that sets are implemented as lists, where each element of a set appears exactly once in the list. Define functions that implement the following operations.
(From ex. 10.11 of Sethi) Fill in the blanks in the following, using the standard Astarte functions, to make the equations true for all x and y. You can define helper functions if you like.
rfold (______, ______) x = length(x)
rfold (______, ______) x = x ++ y (or concat(x,y))
rfold (______, ______) x = map f x