anchor.diff:          else find p t
   
   /// Returns the result of the first successful application of a function to the elements of a list.
  -// OPTIMIZE : Make this an alias for List.tryFind.
  +// OPTIMIZE : Make this an alias for List.tryPick.
   let rec tryfind f l =
       List.tryPick f l
   
  
positive.code: (* ------------------------------------------------------------------------- *)
  
  /// Merges together two sorted lists with respect to a given ordering.
  let rec merge ord l1 l2 = 
      match l1 with
      | [] -> l2
  
negative.code: let flat l = itlist (@) l []
  
  /// Separates the first element of a list to satisfy a predicate from the rest of the list.
  // OPTIMIZE : Rewrite this function using ListZipper from ExtCore.
  let rec remove p l = 
      match l with
      | [] -> failwith "remove"
  