Resco and Small gave the first example of an affine Noetherian algebra which is not finitely presented. It shown that their has no finite-dimensional filtrations whose associated graded algebras are Noetherian, affirming prediction. A modification yields countable fields over ‘almost all’ (that is, a co-countable continuum of) lack such filtration, answer to question suggested by Irving derived.

In this paper we examine the structure of countable closed invariant sets under a dynamical system on a compact metric space. We are motivated by a desire to understand the possible structures of inhomogeneities in one-dimensional non-hyperbolic sets (inverse limits of finite graphs) particularly when those inhomogeneities form a countable set. All of the previous literature regarding the colle...

We exhibit some uncountable groups with Property (FH). In particular, these groups do not have Kazhdan’s Property (T), which is known to be equivalent to Property (FH) for countable groups. Our first examples rely on a theorem of Delzant, which states that every countable group embeds in a group with Property (T). We give two constructions. The first is a (non-explicit) transfinite induction on...

A topological space has calibre ω1 (resp., calibre (ω1,ω)) if every point-countable (resp., point-finite) collection of nonempty open sets is countable. It has compact-calibre ω1 (resp., compact-calibre (ω1,ω)) if, for every family of uncountably many nonempty open sets, there is some compact set which meets uncountably many (resp., infinitely many) of them. It has CCC (resp., DCCC) if every di...

In this paper, we establish the relationships between spaces with a compact-countable weak-base and spaces with various compact-countable networks, and give two mapping theorems on spaces with compact-countable weakbases. Weak-bases and g-first countable spaces were introduced by A.V.Arhangel’skii [1]. Spaces with a point-countable weak-base were discussed in [5,6], and spaces with a locally co...

In [Vau61] Vaught conjectured that a countable first order theory has countably many or 2א0 many countable models. Here, the following special case is proved. Theorem. If T is a superstable theory of finite rank with < 2א0 many countable models, then T has countably many countable models. The basic idea is to associate with a theory a ∧ − definable group G (called the structure group) which con...

We show that the isomorphism relation for countable Boolean algebras is Borel complete, i.e., the isomorphism relation for arbitrary countable structures is Borel reducible to that for countable Boolean algebras. This implies that Ketonen’s classification of countable Boolean algebras is optimal in the sense that the kind of objects used for the complete invariants cannot be improved in an esse...

We prove that a space with a σ-weakly hereditarily closurepreserving sn-network is sn-first countable. As an application of this result, we prove that a Lindelöf space with a σ-weakly hereditarily closurepreserving sn-network is sn-second countable. The above results answer some questions posed by L. Yan. AMS Mathematics Subject Classification (2000): 54D20, 54D65, 54E20, 54E99