anchor.diff:  module NHol.lib
   
   open System
  +open System.Diagnostics
   
   open FSharp.Compatibility.OCaml
   open FSharp.Compatibility.OCaml.Num
  
positive.code:     mapf
  
  /// Computes the last element of a list.
  // OPTIMIZE : Make this an alias for List.last.
  let rec last l = 
      match l with
      | [x] -> x
  
negative.code: (* ------------------------------------------------------------------------- *)
  
  /// Iterates a function a fixed number of times.
  [<Obsolete("Use Choice.funpow instead.")>]
  let rec funpow n f x = 
      if n < 1 then x
      else funpow (n - 1) f (f x)
  