Generating Permutations using LINQ

Question

I have a set of products that must be scheduled. There are P products each indexed from 1 to P. Each product can be scheduled into a time period 0 to T. I need to construct

Answer 1

    public static IList> Permutation(ImmutableList> dimensions)
    {
        IList> result = new List>();
        Step(ImmutableList.Create(), dimensions, result);
        return result;
    }

    private static void Step(ImmutableList previous, 
        ImmutableList> rest, 
        IList> result)
    {
        if (rest.IsEmpty)
        {
            result.Add(previous);
            return;
        }

        var first = rest[0];
        rest = rest.RemoveAt(0);

        foreach (var label in first)
        {
            Step(previous.Add(label), rest, result);
        }
    }