using System;
using System.Linq;
using System.Collections.Generic;
 
public class Test
{
	static void CollectAll(ISet<String> remaining, IList<string> soFar, List<List<string>> all) {
		if (soFar.Count != 0) {
			all.Add(soFar.ToList());
		}
		foreach (var item in remaining.ToList()) {
			remaining.Remove(item);
			soFar.Add(item);
			CollectAll(remaining, soFar, all);
			soFar.Remove(item);
			remaining.Add(item);
		}
	}
	public static void Main()
	{
		var items = new HashSet<string> {"a", "b", "c"};
		var tmp = new List<string>();
		List<List<string>> res = new List<List<string>>();
		CollectAll(items, tmp, res);
		foreach (var lst in res) {
			Console.WriteLine(string.Join(" ", lst.ToArray()));
		}
	}
}

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