public static class ListExtentions
{
	public static IEnumerable Cartesian(this IEnumerable<IEnumerable> items)
	{
		var slots = items
		// initialize enumerators
		.Select(x => x.GetEnumerator())
		// get only those that could start in case there is an empty collection
		.Where(x => x.MoveNext())
		.ToArray();

		while (true)
		{
			// yield current values
			yield return slots.Select(x => x.Current);

			// increase enumerators
			foreach (var slot in slots)
			{
				// reset the slot if it couldn't move next
				if (!slot.MoveNext())
				{
					// stop when the last enumerator resets
					if (slot == slots.Last()) { yield break; }
					slot.Reset();
					slot.MoveNext();
					// move to the next enumerator if this reseted
					continue;
				}
				// we could increase the current enumerator without reset so stop here
				break;
			}
		}
	}
}