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A CO-ANALYTIC COHEN-INDESTRUCTIBLE MAXIMAL COFINITARY GROUP

Published online by Cambridge University Press:  19 June 2017

VERA FISCHER
Affiliation:
KURT GÖDEL RESEARCH CENTER UNIVERSITÄT WIEN, WÄHRINGERSTRAßE 25 1080 WIEN AUSTRIA E-mail: vera.fischer@univie.ac.at
DAVID SCHRITTESSER
Affiliation:
DEPARTMENT OF MATHEMATICAL SCIENCES UNIVERSITY OF COPENHAGEN UNIVERSITETSPARKEN 5 2100 COPENHAGEN DENMARK E-mail:david.s@math.ku.dk
ASGER TÖRNQUIST
Affiliation:
DEPARTMENT OF MATHEMATICAL SCIENCES UNIVERSITY OF COPENHAGEN UNIVERSITETSPARKEN 5 2100 COPENHAGEN DENMARK E-mail: asgert@math.ku.dk
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Abstract

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Assuming that every set is constructible, we find a ${\text{\Pi }}_1^1 $ maximal cofinitary group of permutations of $\mathbb{N}$ which is indestructible by Cohen forcing. Thus we show that the existence of such groups is consistent with arbitrarily large continuum. Our method also gives a new proof, inspired by the forcing method, of Kastermans’ result that there exists a ${\text{\Pi }}_1^1 $ maximal cofinitary group in L.

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Articles
Copyright
Copyright © The Association for Symbolic Logic 2017