Bart Kastermans

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If F ⊆ N N is an analytic family of pairwise eventually different functions then the following strong maximality condition fails: For any countable H ⊆ N N, no member of which is covered by finitely many functions from F , there is f ∈ F such that for all h ∈ H there are infinitely many integers k such that f (k) = h(k). However if V = L then there exists a(More)
We make progress toward solving a long-standing open problem in the area of computable linear orderings by showing that every computable η-like linear ordering without an infinite strongly η-like interval has a computable copy without nontrivial computable self-embedding. The precise characterization of those computable linear order-ings which have(More)
ACKNOWLEDGEMENTS My thanks to the many people whose thoughts have contributed to this thesis and to my mathematical development, including In particular, my collaborations with Tyrrell McAllister and Herb Scarf have been tremendously invaluable. Many thanks to my doctoral committee, especially John Stembridge for his careful reading of this thesis. I am(More)
We consider the possible cardinalities of the following three cardinal invariants which are related to the permutation group on the set of natural numbers: a g := the least cardinal number of maximal cofinitary permutation groups; a p := the least cardinal number of maximal almost disjoint permutation families; c(Sym(N)) := the cofinality of the permutation(More)
Hirschfeldt and Shore have introduced a notion of stability for infinite posets. We define an arguably more natural notion called weak stability, and we study the existence of infinite computable or low chains or antichains, and of infinite Π 0 1 chains and antichains, in infinite computable stable and weakly stable posets. For example, we extend a result(More)
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