anchor.diff:  //    [<ContractInvariantMethod>]
   //    member private this.ObjectInvariant () : unit =
   //        (*   1. length front >= length rear                  *)
  -//        Contract.Invariant (
  -//            LazyList.length front >= rear.Length)
  +//        Contract.Invariant (LazyList.length front >= rear.Length)
   //        (*   2. length pending = length front - length rear  *)
  -//        Contract.Invariant (
  -//            LazyList.length pending = (LazyList.length front - rear.Length))
  +//        Contract.Invariant (LazyList.length pending = (LazyList.length front - rear.Length))
   //        (*   3. (in the absence of insertf's)                *)
   //        (*      pending = nthtail (front, length rear)       *)
   //        // TODO : Determine the best way to implement this last invariant condition.
   //        //
   
  -    /// Performs the 'rotate' operation on a Queue, given the private fields
  -    /// holding the queue elements.
  +    /// Performs the 'rotate' operation on a Queue, given the private fields holding the queue elements.
       static member private Rotate (xs : LazyList<'T>, ys : 'T list, rys : LazyList<'T>) =
           match ys with
           | [] ->
  
positive.code:             let front = Queue<'T>.Rotate (front, rear, LazyList.empty)
              Queue (front, [], front)
          else
              Queue (
                  front,
                  rear,
                  LazyList.tail pending)
  
  /// Functional operators related to the Queue type.
  [<RequireQualifiedAccess; CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
  module Queue =
      //open OptimizedClosures
  
      /// Returns an empty queue of the given type.
      [<CompiledName("Empty")>]
      let empty<'T> : Queue<'T> =
          Queue<'T>.Empty
  
      /// Returns true if the given queue is empty; otherwise, false.
      [<CompiledName("IsEmpty")>]
      let inline isEmpty (queue : Queue<'T>) =
          // Preconditions
  
negative.code:         
          queue.Enqueue value
  
      /// <summary>Returns a new Queue with the object added to the front of the given Queue.</summary>
      /// <param name="value"></param>
      /// <param name="queue"></param>
      /// <returns></returns>
      [<CompiledName("EnqueueFront")>]
      let inline enqueueFront value (queue : Queue<'T>) =
          // Preconditions
  