On a theorem of Baumgartner and Weese
On absolutely divergent series
We show that in the -stage countable support iteration of Mathias forcing over a model of CH the complete Boolean algebra generated by absolutely divergent series under eventual dominance is not isomorphic to the completion of P(ω)/fin. This complements Vojtáš’ result that under the two algebras are isomorphic [15].
On an extremal characterization of partitions
On automorphisms of Boolean algebras embedded in P (ω)/fin
We prove that, under CH, for each Boolean algebra A of cardinality at most the continuum there is an embedding of A into P(ω)/fin such that each automorphism of A can be extended to an automorphism of P(ω)/fin. We also describe a model of ZFC + MA(σ-linked) in which the continuum is arbitrarily large and the above assertion holds true.
On axial maps of direct product,s I
On axial maps of direct products, II
On CCC boolean algebras and partial orders
We partially strengthen a result of Shelah from [Sh] by proving that if and is a CCC partial order with e.g. (the successor of ) and then is -linked.
On characteristic sets of a system of equivalence relations
On chromatic number of product of graphs
On Ciesielski's problems.
On club-like principles on regular cardinals above
On collections of almost disjoint families
On dense subsets of rational numbers
On diamond sequences
On FU()-spaces and -sequential spaces
Following Kombarov we say that is -sequential, for , if for every non-closed subset of there is such that and . This suggests the following definition due to Comfort and Savchenko, independently: is a FU()-space if for every and every there is a function such that . It is not hard to see that ( denotes the Rudin–Keisler order) every -sequential space is -sequential every FU()-space is a FU()-space. We generalize the spaces to construct examples of -sequential...
On full Suslin trees
On infinite partitions of lines and space
Given a partition P:L → ω of the lines in , n ≥ 2, into countably many pieces, we ask if it is possible to find a partition of the points, , so that each line meets at most m points of its color. Assuming Martin’s Axiom, we show this is the case for m ≥ 3. We reduce the problem for m = 2 to a purely finitary geometry problem. Although we have established a very similar, but somewhat simpler, version of the geometry conjecture, we leave the general problem open. We consider also various generalizations...
On invariant CCC -ideals
On isomorphisms between -ideals on
On (m, n)-ramifications or (m, n)-pseudo-trees of sets.