The chain covering number of a poset with no infinite antichains

Uri Abraham; Maurice Pouzet

doi:10.5802/crmath.511

Combinatoire

The chain covering number of a poset with no infinite antichains
[Le nombre de chaînes recouvrant un ensemble ordonné sans antichaînes infinies]

Uri Abraham ¹ ; Maurice Pouzet ^2,³

¹ Math & CS Dept., Ben-Gurion University, Beer-Sheva, 84105 Israel
² ICJ, Mathématiques, Université Claude-Bernard Lyon1, 43 bd. 11 Novembre 1918, 69622 Villeurbanne Cedex, France
³ Mathematics & Statistics Department, University of Calgary, Calgary, Alberta, Canada T2N 1N4

Comptes Rendus. Mathématique, Volume 361 (2023), pp. 1383-1399.

Résumé
Abstract

Le nombre de recouvrement par chaînes d’un ensemble ordonné $P$ (poset), noté $Cov (P)$ , est le plus petit nombre de chaînes nécessaires pour recouvrir $P$ . Pour un cardinal donné $ν$ , on donne une liste de posets $Q$ de nombre de recouvrement par chaînes $ν$ telle que pour tout poset $P$ sans antichaîne infinie, $Cov (P) \geq ν$ si et seulement si $P$ contient une copie d’un membre de la liste. Cette liste est constituée de posets de cardinal $ν$ , elle a deux éléments si $ν$ est un cardinal successeur, à savoir ${[ν]}^{2}$ et son dual, et quatre éléments si $ν$ est un cardinal limite avec $cf (ν)$ faiblement compact. Pour $ν = ℵ_{1}$ , une liste a été donnée par le premier auteur ; sa construction a été étendue par F. Dorais à tout cardinal successeur infini $ν$ .

The chain covering number $Cov (P)$ of a poset $P$ is the least number of chains needed to cover $P$ . For an uncountable cardinal $ν$ , we give a list of posets of cardinality and covering number $ν$ such that for every poset $P$ with no infinite antichain, $Cov (P) \geq ν$ if and only if $P$ embeds a member of the list. This list has two elements if $ν$ is a successor cardinal, namely ${[ν]}^{2}$ and its dual, and four elements if $ν$ is a limit cardinal with $cf (ν)$ weakly compact. For $ν = ℵ_{1}$ , a list was given by the first author; his construction was extended by F. Dorais to every infinite successor cardinal $ν$ .

Reçu le : 2023-04-03
Révisé le : 2023-06-08
Accepté le : 2023-06-09
Publié le : 2023-10-31

DOI : 10.5802/crmath.511

Classification : 03E05, 06A07

Affiliations des auteurs :

Uri Abraham ¹ ; Maurice Pouzet ^{2, 3}

¹ Math & CS Dept., Ben-Gurion University, Beer-Sheva, 84105 Israel
² ICJ, Mathématiques, Université Claude-Bernard Lyon1, 43 bd. 11 Novembre 1918, 69622 Villeurbanne Cedex, France
³ Mathematics & Statistics Department, University of Calgary, Calgary, Alberta, Canada T2N 1N4

Licence :

CC-BY 4.0

Droits d'auteur : Les auteurs conservent leurs droits

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     title = {The chain covering number of a poset with no infinite antichains},
     journal = {Comptes Rendus. Math\'ematique},
     pages = {1383--1399},
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     year = {2023},
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Uri Abraham; Maurice Pouzet. The chain covering number of a poset with no infinite antichains. Comptes Rendus. Mathématique, Volume 361 (2023), pp. 1383-1399. doi : 10.5802/crmath.511. https://comptes-rendus.academie-sciences.fr/mathematique/articles/10.5802/crmath.511/

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