5 papers
Disjoint Non-Free Subgoups of Abelian Groups
Andreas Blass, Saharon Shelah
Let G be an abelian group and let lambda be the smallest rank of any group whose direct sum with a free group is isomorphic to G. If lambda is uncountable, then G has lambda pairwi…
Ultrafilters and partial products of infinite cyclic groups
Andreas Blass, Saharon Shelah
We consider, for infinite cardinals kappa and alpha <= kappa^+, the group Pi(kappa,< alpha) of sequences of integers, of length kappa, with non-zero entries in fewer than alpha pos…
On Polynomial Time Computation Over Unordered Structures
Andreas Blass, Yuri Gurevich, Saharon Shelah
This paper is motivated by the question whether there exists a logic capturing polynomial time computation over unordered structures. We consider several algorithmic problems near…
Mobius functions of lattices
Andreas Blass, Bruce E. Sagan
We introduce the concept of a bounded below set in a lattice. This can be used to give a generalization of Rota's broken circuit theorem to any finite lattice. We then show how thi…
Characteristic and Ehrhart polynomials
Andreas Blass, Bruce E. Sagan
Let A be a subspace arrangement and let chi(A,t) be the characteristic polynomial of its intersection lattice L(A). We show that if the subspaces in A are taken from L(B_n), where…