type 'a tree =  | Lf
                | Br of 'a * 'a tree * 'a tree
let rec f(n,t) =
    match t with
    | Lf -> Lf
    | Br(a,t1,t2) -> if n>0 then Br(a, f(n-1, t1), f((n-1), t2))
                            else Lf
let rec g p = function
    | Br(a, t1, t2) when p a -> Br(a, g p t1, g p t2)
    | _ -> Lf;;
let rec h k = function
    | Lf -> Lf
    | Br(a, t1, t2) -> Br(k a, h k t1, h k t2);;