[seqfan] Re: When are stereoisomers counted in A000628?

bradklee at gmail.com bradklee at gmail.com
Thu Feb 9 14:42:31 CET 2017


Yes, but your word "symmetric" still confuses me. When describing symmetry of a geometric model, I would say invariant / covariant with regard to a particular representation, usually irreducible. 

With A000628, I am also slightly confused by the comment, should it rather say: "acts invariantly at each node" or "means that the invariant transformation group of each node is A4 rather than the full S4"?

A picture or ASCII drawing might help to clarify the meaning.

Brad

> On Feb 9, 2017, at 5:55 AM, Richard J. Mathar <mathar at mpia-hd.mpg.de> wrote:
> 
> With reference to http://list.seqfan.eu/pipermail/seqfan/2017-February/017255.html:
> 
> The phrase is not useful in both cases, because it is not important with which
> group you act on the molecule (you can act with any geometric group on any
> molecule if you wish) but whether that molecule is symmetric (an "eigenvector")
> or non-symmetric upon action of the symmetry group.
> 
> What the comment means to say is (?) that in A000628 molecules are counted if
> they are not symmetric under actions of S_4, whereas they are counted in
> A000602 if they are not symmetric under actions of A_4.
> 
> 
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