# A thin-tall boolean algebra which is isomorphic to each of its uncountable subalgebras

Robert Bonnet, Matatyahu Rubin

Research output: Contribution to journalArticlepeer-review

## Abstract

Theorem A{lozenge, open}א1There is a Boolean algebra B with the following properties:(1)B is thin-tall, and(2)B is downward-categorical. That is, every uncountable subalgebra of B is isomorphic to B. The algebra B from Theorem A has some additional properties. For an ideal K of B, set cmplB(K):={a∈B|a.b=0 for all b∈K}. We say that K is almost principal if K∪cmplB(K) generates B.(3)B is rigid in the following sense. Suppose that I, J are ideals in B and f:B/I→B/J is a homomorphism with an uncountable range. Then there is an almost principal ideal K of B such that |cmpl(K)|≤א0, I∩K⊆J∩K, and for every a∈K, f(a/I)=a/J.(4)The Stone space of B is sub-Ostaszewski. Boolean-algebraically, this means that: if I is an uncountable ideal in B, then B/I has cardinality ≤א0.(5)Every uncountable subalgebra of B contains an uncountable ideal of B.(6)Every subset of B consisting of pairwise incomparable elements has cardinality ≤א0.(7)Every uncountable quotient of B has properties (1)-(6).Assuming {lozenge, open}א1 we also construct a Boolean algebra C such that:. (1)C has properties (1) and (4)-(6) from Theorem A, and every uncountable quotient of C has properties (1) and (4)-(6).(2)C is rigid in the following stronger sense. Suppose that I, J are ideals in C and f:C/I→C/J is a homomorphism with an uncountable range. Then there is a principal ideal K of C such that |cmpl(K)|≤א0, I∩K⊆J∩K, and for every a∈K, f(a/I)=a/J.

Original language English 1503-1525 23 Topology and its Applications 158 13 https://doi.org/10.1016/j.topol.2011.05.003 Published - 15 Aug 2011

## Keywords

• Ostaszewski space
• Rigid boolean algebra
• Scattered space
• Superatomic boolean algebra
• Thin-tall

## ASJC Scopus subject areas

• Geometry and Topology

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