Give the most general types of the following functions. Again, try figuring each out yourself, but you can check yourself with OCaml. a) let f1 (x, y) (y, x) (Hint: you may need two type variables) b) let f2 x y = [[x]; y] c) let f3 x y z = [x::z; y::z] d) let f4 x y [x; x + y) e) let rec f5 x = match x with [] -> [] | x::t -> [x; x]::(f5 t)