Time scheduler in C#

using System;
using System.Collections.Generic;
using System.Text;

namespace Idaligo.Time
{
	public class OverAreaSequence : ISequence
	{
		private ISequence sequence;
		private IArea area;

		public OverAreaSequence(ISequence sequence, IArea area)
		{
			if (sequence == null) throw new ArgumentNullException("sequence");
			if (area == null) throw new ArgumentNullException("area");
			this.sequence = sequence;
			this.area = area;
		}

		public bool AtPoint(DateTime at)
		{
			return this.sequence.AtPoint(at) && this.area.Hit(at);
		}

		public IEnumerable<DateTime> Walk(DateTime from)
		{
			IEnumerator<TimeRange> iteratorForArea = this.area.Walk(from).GetEnumerator();
			if (iteratorForArea.MoveNext())
			{
				TimeRange area = iteratorForArea.Current;

				DateTime start = (iteratorForArea.Current.From < from) ? from : iteratorForArea.Current.From;
				IEnumerator<DateTime> iteratorForSequence = this.sequence.Walk(start).GetEnumerator();
				while (iteratorForSequence.MoveNext())
				{
					DateTime at = iteratorForSequence.Current;
					if (at < area.Till)
					{
						yield return at;
					}
					else
					{
						break;
					}
				}


				while (iteratorForArea.MoveNext())
				{
					area = iteratorForArea.Current;
					iteratorForSequence = this.sequence.Walk(area.From).GetEnumerator();
					while (iteratorForSequence.MoveNext())
					{
						DateTime at = iteratorForSequence.Current;
						if (at < area.Till)
						{
							yield return at;
						}
						else
						{
							break;
						}
					}
				}
			}
		}
	}
}