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Heike Mildenberger

Publications and source records attributed to Heike Mildenberger.

23 records · Page 2Linked to original sources
arXiv2000

The splitting number can be smaller than the matrix chaos number

Let chi be the minimum cardinal of a subset of 2^omega that cannot be made convergent by multiplication with a single Toeplitz matrix. By an application of creature forcing we show that s<chi is consistent. We thus answer a question by Vojtas. We give two kinds of models for the strict inequality. The first is the combination of an aleph_2-iteration of some proper forcing with adding aleph_1 random reals. The second kind of models is got by adding delta random reals to a model of MA_{< kappa} for some delta in [aleph_1,kappa). It was a conjecture of Blass that s=aleph_1<chi=kappa holds in such a model. For the analysis of the second model we again use the creature forcing from the first model.

math.LO↗
arXiv1999

On absolutely divergent series

We show that in the aleph_2-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(omega)/fin. This complements Vojtas' result, that under cf(c)=p the two algebras are isomorphic

math.LO↗
arXiv1999

Changing cardinal characteristics without changing omega-sequences or cofinalities

We show: There are pairs of universes V_1 subseteq V_2 and there is a notion of forcing P in V_1 such that the change mentioned in the title occurs when going from V_1[G] to V_2[G] for a P-generic filter G over V_2. We use forcing iterations with partial memories. Moreover, we implement highly transitive automorphism groups into the forcing orders.

math.LO↗
arXiv1996

On the cofinality of ultrapowers

All ultrafilters under consideration here are non-principal ultrafilters on the set omega of natural numbers. We are concerned with the possible cofinalities of ultrapowers of omega with respect to such ultrafilters. We show that no cardinal below the groupwise density number g can occur as such a cofinality and that at most one cardinal below the splitting number s can so occur. The proof for s, when combined with a result of Nyikos, gives the additional information that all P_{kappa}-point ultrafilters, for kappa greater than the bounding number b, are nearly coherent.

math.LO↗