Category Archives: exposition

a post aimed to teach something

A family of non-synchronizing groups

As I explained recently, according to the O’Nan–Scott Theorem, a finite primitive permutation group either preserves a Cartesian structure, or is of affine, diagonal or almost simple type. In all these types except the last, the action of the group … Continue reading

Posted in exposition, symmetric group | Tagged , , , , , , , | Leave a comment

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

Posted in doing mathematics, exposition, mathematics | Tagged , , , , , , , , , | Leave a comment


There are various overused terms in mathematics. “Normal” is one of them. Perhaps the four commonest uses are the following: A complex square matrix is normal if it commutes with its conjugate transpose. Normal matrices are precisely the ones which … Continue reading

Posted in exposition | Tagged , , , , , | 3 Comments

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

Posted in exposition, synchronization | Tagged , , , , , , , | Leave a comment

A mathematical promenade

I haven’t posted for a while; I have been in China where the firewall allows me to read WordPress but not to post. Normal service now resumed (hopefully). Given four real polynomials, all of which vanish at the origin, suppose … Continue reading

Posted in books, exposition | Tagged , , , | 1 Comment

Dugald Macpherson’s birthday meeting

Still catching up on the backlog: last week I was in Edinburgh for a meeting at ICMS for Dugald Macpherson’s birthday. The ICMS has just moved to new premises at the top of the University of Edinburgh’s new Bayes Centre, … Continue reading

Posted in events, exposition | Tagged , , , , , , , , | Leave a comment

The existential transversal property

One of the first things that João Araújo introduced me to when we started collaborating, after synchronization, was the universal transversal property: a permutation group G on the set {1,…,n} has the k-universal transversal property (k-ut for short) if, given … Continue reading

Posted in exposition | Tagged , , , | Leave a comment