/// <summary>
/// Cancels the prvious rally.
/// </summary>
public IEnumerable <Receive> CancelRally()
{
if (Points.Count < 1)
{
throw new InvalidOperationException("Cannot rollback from empty state!");
}
var point = Points.Last();
Points.Remove(point);
PointCounter.Rollback();
(PointA, PointB) = (PointCounter.PointA, PointCounter.PointB);
OnRallyCanceled(point);
return(point.Receives);
}