Calendar.cs

public class Calendar : Story
{
    private string _region;
    private readonly ISet<Event> _events;

    public Calendar(Guid id, string region)
    {
        Id = id;
        
        _region = region;
        _events = new HashSet<Event>();
    }

    public Event Schedule(User contributor, EventDetail detail)
    {
        var @event = EventFactory.Create(this, contributor, detail);

        _events.Add(@event);

        return @event;
   }
}