 
   /// Change the state of this `TBD` from `.waiting` to `.executing`
 
-  public override func beginExecution()
+  open override func beginExecution()
   {
     super.beginExecution()
   }

  /// - returns: whether the cancellation was performed successfully.

  @discardableResult
  public func cancel(_ reason: String = "") -> Bool
  {
    return determine(Result.error(DeferredError.canceled(reason)))
  }

  ///
  /// - parameter task:  the closure to be enqueued

  open func notify(qos: DispatchQoS? = nil, task: @escaping (Result<Value>) -> Void)
  {
    var c = resultp.load(order: .acquire)
    if c == nil
