interface Subscription {

    // Cancels the subscription
    unsubscribe() : void;

    // A boolean value indicating whether the subscription is closed
    get closed() : Boolean;
}

interface ObservableSubscription {
  /** A boolean flag indicating whether the subscription is closed.
   * @remarks
   * When `true`, the subscription will not issue new values to the {@link ObservableObserver} and
   * has terminated. No new values are expected.
   *
   * @readonly
   */
  closed?: boolean;
  /** Cancels the subscription.
   * @remarks
   * This cancels the ongoing subscription and the {@link ObservableObserver}'s callbacks will
   * subsequently not be called at all. The subscription will be terminated and become inactive.
   */
  unsubscribe(): void;
}