LINQ implementation of Cartesian Product with pruning

Question

I hope someone is able to help me with what is, at least to me, quite a tricky algorithm.

The Problem

I have a List (1 <= size <= 5, but siz

Answer 1

The finalised solution to the whole combining of multisets, then pruning the result-sets to remove duplicates problem ended up in a helper class as a static method. It takes svick's much appreciated answer and injects the IEqualityComparer dependency into the existing CartesianProduct answer I found at Eric Lipperts's blog here (I'd recommend reading his post as it explains the iterations in his thinking and why the linq implimentation is the best).

static IEnumerable> CartesianProduct(IEnumerable> sequences,
                                                       IEqualityComparer> sequenceComparer)
{
    IEnumerable> emptyProduct = new[] { Enumerable.Empty() };
    var resultsSet = sequences.Aggregate(emptyProduct, (accumulator, sequence) => from accseq in accumulator
                                                                                  from item in sequence
                                                                                  select accseq.Concat(new[] { item }));

    if (sequenceComparer != null)
        return resultsSet.Distinct(sequenceComparer);
    else
        return resultsSet;
}