Tag Archives: Pablo Spiga

The road closure property

My work with João Araújo and other semigroup theorists has produced a number of permutation group properties which lie between primitivity and 2-homogeneity, especially the synchronization family. Another of these is the road closure propery, which I have discussed here … Continue reading

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The Hall–Paige conjecture

A Latin square of ordern is an n×n array of symbols from an alphabet of size n with the property that each symbol in the alphabet occurs once in each row or column. Two Latin squares L and M are … Continue reading

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Synchronization update

There is some recent news about the synchronization project. Two steps forward have occurred. The set-up Here is a brief recapitulation. Let G be a transitive permutation group on Ω, where |Ω| = n. We say that G is non-synchronizing if there … Continue reading

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Summer school at Marienheide

Last week, I was lecturing at a summer school in Franz Dohrmann Haus, a very pleasant conference centre in the small town of Marienheide, not far from Köln. Apart from a walk on Wednesday afternoon, I didn’t get much exercise, … Continue reading

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Two publications

I don’t think it happened to me before that two of my papers were “published” on the same day. Fortunately, it didn’t happen on April Fools’ Day … One is my paper with Pablo Spiga on switching classes. I described … Continue reading

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Primitive switching classes

Last year I wrote here about switching classes of graphs for which the switching class has a primitive automorphism group. (I repeat the definitions briefly below.) I conjectured that, except for the trivial switching classes of the complete and null … Continue reading

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Automorphism groups of hypergraphs

I am getting old and forgetful, but I don’t think I said anything here about this problem yet. If I did, apologies for the repetition – but there is something new to report! In April, Laci Babai and I finally … Continue reading

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