A class of symmetric difference-closed sets related to commuting involutions
Une classe d'ensembles qui sont fermés sous l'opération de différence symétrique lié aux involutions commutant
Résumé
Recent research on the combinatorics of finite sets has explored the structure of symmetric difference-closed sets, and recent research in combinatorial group theory has concerned the enumeration of commuting involutions in $S_n$ and $A_n$. In this article, we consider an interesting combination of these two subjects, by introducing classes of symmetric difference-closed sets of elements which correspond in a natural way to commuting involutions in $S_n$ and $A_n$. We consider the natural combinatorial problem of enumerating symmetric difference-closed sets consisting of subsets of a set consisting of pairwise disjoint 2-subsets of $[n]$. We prove an explicit combinatorial formula for the number of symmetric difference-closed 4-sets satisfying this property, and we prove an explicit combinatorial formula for an analogous class of symmetric difference-closed sets consisting of elements which correspond to commuting involutions in $A_n$.
Domaines
Combinatoire [math.CO]
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A class of symmnetric difference-closed sets related to commuting involutions.pdf (136.55 Ko)
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