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ON WIDE ARONSZAJN TREES IN THE PRESENCE OF MA

Part of: Set theory

Published online by Cambridge University Press:  07 September 2020

MIRNA DŽAMONJA
Affiliation:
INSTITUT D'HISTOIRE ET DE PHILOSOPHIE DES SCIENCES ET DES TECHNIQUES (IHPST) CNRS & UNIVERSITÉ PANTHÉON-SORBONNE 13 RUE DE FOUR, 75006 PARIS, FRANCE INSTITUTE OF MATHEMATICS CZECH ACADEMY OF SCIENCES ITNÁ 25, 115 76 PRAGUE, CZECH REPUBLIC E-mail: M.Dzamonja@uea.ac.uk URL: mirna.dzamonja@univ-paris1.fr
SAHARON SHELAH
Affiliation:
DEPARTMENT OF MATHEMATICS HEBREW UNIVERSITY OF JERUSALEM 91904, GIVAT RAM, ISRAEL E-mail:shelah@math.huji.ac.il URL: http://shelah.logic.at

Abstract

A wide Aronszajn tree is a tree of size and height $\omega _{1}$ with no uncountable branches. We prove that under $MA(\omega _{1}\!)$ there is no wide Aronszajn tree which is universal under weak embeddings. This solves an open question of Mekler and Väänänen from 1994.

We also prove that under $MA(\omega _{1}\!)$, every wide Aronszajn tree weakly embeds in an Aronszajn tree, which combined with a result of Todorčević from 2007, gives that under $MA(\omega _{1}\!)$ every wide Aronszajn tree embeds into a Lipschitz tree or a coherent tree. We also prove that under $MA(\omega _{1}\!)$ there is no wide Aronszajn tree which weakly embeds all Aronszajn trees, improving the result in the first paragraph as well as a result of Todorčević from 2007 who proved that under $MA(\omega _{1}\!)$ there are no universal Aronszajn trees.

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Copyright
© The Association for Symbolic Logic 2020

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