using System;
using System.Collections.Generic;
 
public class Test
{
	static IEnumerator<string> Generate()
	{
		yield return "A";
		yield return "B";
		yield return "C";
	}
 
	public static void Main()
	{
		using (var iterator = Generate())
		while (iterator.MoveNext())
		{
			Console.WriteLine(iterator.Current);
			if (iterator.Current == "B")
			{
                while (iterator.MoveNext())
		            Console.WriteLine("    " + iterator.Current);
			}
		}
	}
}

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