public virtual IList<AbstractTask> GetReschedulableTasks() {

            return Tasks.Where(abstractTask => abstractTask.State != TaskState.Uninitialized &&
                                                   abstractTask.State != TaskState.Cancelled &&
                                                   abstractTask.State != TaskState.Completed).ToList();

        }

        /// <summary>
        /// All active tasks related to the current snapshot of the timeline.
        /// Active tasks can be modified and rescheduled.
        /// </summary>
        public virtual IList<AbstractTask> CancelableTasks
        {

            get
            {
                return Tasks.Where(abstractTask => abstractTask.State != TaskState.Uninitialized &&
                                                   abstractTask.State != TaskState.Cancelled &&
                                                   abstractTask.State != TaskState.Completed).ToList();
            }
        }

        /// <summary>
        /// All active tasks related to the timeline.  Active tasks can be modified and rescheduled.
        /// </summary>
        public virtual IList<AbstractTask> ActiveTasks
        {
            get
            {
                return Tasks.Where(abstractTask => abstractTask.State != TaskState.Uninitialized &&
                                                   abstractTask.State != TaskState.Cancelled &&
                                                   abstractTask.State != TaskState.Completed).ToList();
            }
        }