class CompoundEnumerator2<T1, T2, T3> : IEnumerator<Tuple<T1, T2, T3>>
{
    Tuple<IEnumerator<T1>, IEnumerator<T2>, IEnumerator<T3>> enumeratorsTuple;
    IEnumerable<System.Collections.IEnumerator> enumerators;
    bool fresh = true;

    public Tuple<T1, T2, T3> Current
    {
        get { return Tuple.Create(enumeratorsTuple.Item1.Current, enumeratorsTuple.Item2.Current, enumeratorsTuple.Item3.Current); }
    }
    object System.Collections.IEnumerator.Current { get { return Current; } }

    public CompoundEnumerator2(Tuple<IEnumerable<T1>, IEnumerable<T2>, IEnumerable<T3>> sets)
    {
        enumeratorsTuple = Tuple.Create(sets.Item1.GetEnumerator(), sets.Item2.GetEnumerator(), sets.Item3.GetEnumerator());
        enumerators = new List<System.Collections.IEnumerator>() { enumeratorsTuple.Item1, enumeratorsTuple.Item2, enumeratorsTuple.Item3 };
    }

    public bool MoveNext()
    {
        if (fresh)
        {
            var canMove = enumerators.All(e => e.MoveNext());
            fresh = !canMove;
            return canMove;
        }

        foreach (var e in enumerators)
        {
            if (e.MoveNext())
                return true;
            e.Reset();
            e.MoveNext();
        }
        return false;
    }

    public void Dispose()
    {
        foreach (var e in enumerators)
            ((IDisposable)e).Dispose();
    }

    public void Reset()
    {
        fresh = true;
        foreach (var e in enumerators)
            e.Reset();
    }
}

static IEnumerable<Tuple<T1, T2, T3>> CrossProduct2<T1, T2, T3>(IEnumerable<T1> set1, IEnumerable<T2> set2, IEnumerable<T3> set3)
{
    using (var enumerator = new CompoundEnumerator2<T1, T2, T3>(Tuple.Create(set1, set2, set3)))
    {
        while (enumerator.MoveNext())
            yield return enumerator.Current;
    }
}