Mikael Hansson

activity

20152023

collaborators

5 papers

math.CO2023

Fixed elements of pircon automorphisms

Mikael Hansson, Vincent Umutabazi

We prove that the subposet induced by the fixed elements of any automorphism of a pircon is also a pircon. By a result of Abdallah, Hansson, and Hultman, the order complex of any o…

math.CO2017

Topology of posets with special partial matchings

Nancy Abdallah, Mikael Hansson, Axel Hultman

Special partial matchings (SPMs) are a generalisation of Brenti's special matchings. Let a \emph{pircon} be a poset in which every non-trivial principal order ideal is finite and a…

math.CO2017

A word property for twisted involutions in Coxeter groups

Mikael Hansson, Axel Hultman

Given an involutive automorphism $θ$ of a Coxeter system $(W, S)$ , let $I (θ) \subseteq W$ denote the set of twisted involutions. We provide a minimal set of moves that ca…

math.CO2016

Generalised Ramsey numbers for two sets of cycles

Mikael Hansson

We determine several generalised Ramsey numbers for two sets $Γ_{1}$ and $Γ_{2}$ of cycles, in particular, all generalised Ramsey numbers $R (Γ_{1}, Γ_{2})$ such that $Γ_{1}$ or $Γ_{2}$ contains…

math.CO2015

The Bruhat order on conjugation-invariant sets of involutions in the symmetric group

Mikael Hansson

Let $I_{n}$ be the set of involutions in the symmetric group $S_{n}$ , and for $A \subseteq {0, 1, \dots, n}$ , let \[ F_n^A=\{σ\in I_n \mid \text{ $σ$ has $a$ fixed points for some $a \i…