anchor.diff:  (* Install a trivial printer for the general polymorphic case.               *)
   (* ------------------------------------------------------------------------- *)
   
  +/// Print a finite partial function.
   let print_fpf(f : func<'a, 'b>) = "<func>"
   
   #if INTERACTIVE
  
positive.code:         with
          | Failure _ -> tryfind f t
  
  // OPTIMIZE : Make this an alias for List.concat.
  let flat l = itlist (@) l []
  
  // OPTIMIZE : Rewrite this function using a list-based zipper.
  let rec remove p l = 
      match l with
  
negative.code:             else h :: t'
          else t'
  
  /// Separates a list into two lists using a predicate.
  // OPTIMIZE : Make this an alias for List.partition.
  let rec partition p l = 
      match l with
  