Simple Many to Many design

	public class TrainLine
	{
	private readonly List<Station> stations = new List<Station>();
	public IEnumerable<Station> Stations
	{
	get { return stations; }
	}
	public void AddStation(Station station)
	{
	stations.Add(station);
	station.AddTrainLine(this);
	}
	public void RemoveStation(Station station)
	{
	stations.Remove(station);
	station.RemoveTrainLine(this);
	}
	}
	public class Station
	{
	private readonly List<TrainLine> trainLines = new List<TrainLine>();
	public IEnumerable<TrainLine> TrainLines
	{
	get { return trainLines; }
	}
	public void AddTrainLine(TrainLine trainLine)
	{
	trainLines.Add(trainLine);
	}
	public void RemoveTrainLine(TrainLine trainLine)
	{
	trainLines.Remove(trainLine);
	trainLine.RemoveStation(this);
	}
	}

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A linked list would be a more logical representation of stations for a train line but for this example we’re using a list.