Category Archives: Olds

Vignettes. Part 11.

There is a body of results in higher category theory which this expository blog post will present you a toy version of. Not to bias this post too much, and not to slight said body of results (they actually are … Continue reading

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Vignettes. Part 9. Two different meanings of “star hypergraph”.

This little post is meant to be technically useful, pointing out one of the myriad clashes of terminology that exist in just about any science. I happenend to know the term “star hypergraph” for a long time, but only in … Continue reading

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Compressing and summarizing. Part 0.

Some are of the opinion that blogs add noise to the internet and make good information harder to find. There certainly is something to this view, but I think by and large blogs are to the good, when done well. … Continue reading

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Vignettes. Part 8.

The following is an illustration of a very widely known, yet not widely-enough-known basic connection between things. Explanations will not be given. They can easily be found, given internet access. This connection gives a structure and systematic explanation for some … Continue reading

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Vignettes. Part 6.

If one cares for categories, one should intentionally take an intensional view on them:  axioms matter. In particular, associativity is an axiom. But it is excusable that one sometimes forgets that associativity is axiomatic: so many categories are concretizable (and then, … Continue reading

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Vignettes. Part 5.

Arguably the simplest non-trivial example of an unlabelled simple undirected graph which is not reconstructible from its vertex-deleted subgraphs is the -regular tree, illustrated in parts by Needfull to say: that you only see five neighbors at each vertex is … Continue reading

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Vignettes. Part 4.

I would not have believed that Kurt Gödel once felt it necessary to explain to Ernst Zermelo “Ein Negationsstrich hat ja nur Sinn über einer Zeichenverbindung, die eine Behauptung ausdrückt (über der Ziffer 5 etwa ist ein Negationsstrich sinnlos).”, yet, … Continue reading

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