Question about None

Andre Engels andreengels at
Sun Jun 14 19:26:31 CEST 2009

On Sun, Jun 14, 2009 at 6:49 PM, Paul
LaFollette<paul.lafollette at> wrote:
> Now, suppose that I want to generate, say, the set of all ordered
> trees with N nodes.   I need to be able to represent the empty ordered
> tree, i.e. the tree with with zero nodes.  There are a lot of ways I
> could do this.  The problem is that I might tomorrow be looking
> instead at rooted trees, or free trees, or Young tableaux and in each
> case I will need to represent the empty rooted tree, or the empty free
> tree, or the empty Young tableau.
> In a very real sense, the empty Young tableau IS a Young tableau and
> the empty ordered tree IS an ordered tree.  But in an equally real
> sense they are the same "ghost of a thing" looked at in different
> universes of discourse.

But do you also want the empty Young tableau to BE an ordered tree? A
number? A diddlewoodaddy? It seems much more logical to me to define
your Young tableaus such that the definition includes the empty one as

André Engels, andreengels at

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