McAloon showed that if 𝓐 is a nonstandard model of IΔ₀, then some initial segment of 𝓐 is a nonstandard model of PA. Sommer and D'Aquino characterized, in terms of the Wainer functions, the elements that can belong to such an initial segment. The characterization used work of Ketonen and Solovay, and Paris. Here we give conditions on a model 𝓐 of IΔ₀ guaranteeing that there is an n-elementary initial segment that is a nonstandard model of PA. We also characterize the elements that can be included....

We analyze several “strong meager” properties for filters on the natural numbers between the classical Baire property and a filter being $F_{\sigma }$. Two such properties have been studied by Talagrand and a few more combinatorial ones are investigated. In particular, we define the notion of a P⁺-filter, a generalization of the traditional concept of P-filter, and prove the existence of a non-meager P⁺-filter. Our motivation lies in understanding the structure of filters generated by complements of members...

We develop a theory of sharp measure zero sets that parallels Borel’s strong measure zero, and prove a theorem analogous to Galvin–Mycielski–Solovay theorem, namely that a set of reals has sharp measure zero if and only if it is meager-additive. Some consequences: A subset of $2^{\omega }$ is meager-additive if and only if it is $ℰ$-additive; if $f:2^{\omega }\to 2^{\omega }$ is continuous and $X$ is meager-additive, then so is $f\left(X\right)$.

We define an equivalent variant $L{K}_{sp}$ of the Gentzen sequent calculus $LK$. In $L{K}_{sp}$ weakenings or contractions can be performed in parallel. This modification allows us to interpret a symmetrical system of mix elimination rules ${}_{L{K}_{sp}}$ by a finite rewriting system; the termination of this rewriting system can be machine checked. We give also a self-contained strong normalization proof by structural induction. We give another strong normalization proof by a strictly monotone subrecursive interpretation; this interpretation...

In §1 we define some properties of ideals by using games. These properties strengthen precipitousness. We call these stronger ideals. In §2 we show some limitations on the existence of such ideals over ${}_{\kappa }\lambda$. We also present a consistency result concerning the existence of such ideals over ${}_{\kappa }\lambda$. In §3 we show that such ideals satisfy stronger normality. We show a cardinal arithmetical consequence of the existence of strongly normal ideals. In § 4 we study some “large cardinal-like” consequences of stronger...

The relations M(κ,λ,μ) → B [resp. B(σ)] meaning that if $A\subset {\left[\kappa \right]}^{\lambda }$ with |A|=κ is μ-almost disjoint then A has property B [resp. has a σ-transversal] had been introduced and studied under GCH in [EH]. Our two main results here say the following: Assume GCH and let ϱ be any regular cardinal with a supercompact [resp. 2-huge] cardinal above ϱ. Then there is a ϱ-closed forcing P such that, in $V^P$, we have both GCH and $M({\varrho }^{(+\varrho +1)},{\varrho }^{+},\varrho )\nrightarrow B$ [resp. $M({\varrho }^{(+\varrho +1)},\lambda ,\varrho )\nrightarrow B\left({\varrho }^{+}\right)$ for all $\lambda \le {\varrho }^{(+\varrho +1)}]$. These show that, consistently, the results of [EH] are sharp. The necessity...

A group G is strongly bounded if every isometric action of G on a metric space has bounded orbits. We show that the automorphism groups of typical countable structures with the small index property are strongly bounded. In particular we show that this is the case when G is the automorphism group of the countable universal locally finite extension of a periodic abelian group.

We study connections between G-compactness and existence of strongly determined types.

Let $X\subseteq 2^w$. Consider the class of all Borel $F\subseteq X\times 2^w$ with null vertical sections $F_x$, x ∈ X. We show that if for all such F and all null Z ⊆ X, ${\cup }_{x\in Z}{F}_x$ is null, then for all such F, ${\cup }_{x\in X}{F}_x\ne 2^w$. The theorem generalizes the fact that every Sierpiński set is strongly meager and was announced in [P].

À travers l'étude d'un modèle de représentation des connaissances comme catégorie de faisceaux de traits localement définis ; ce texte montre que la théorie des topoï permet de décrire formellement l'émergence d'une logique intrinsèque à partir d'une approche relationnelle, qu'elle soit structurale ou cognitive. On peut alors caractériser mathématiquement le défaut d'intensionnalité des modèles classiques, et montrer qu'une solution est dans la mathématisation de structures entièrement relationnelles....

Un système de règles grammaticales est présenté pour analyser un fragment du français permettant l'expression de théorèmes et de preuves mathématiques. Pour cet objectif, on développe une version de la grammaire de Montague, avec des catégories syntaxiques relatives au contexte et aux domaines d'individus. Ce système peut être interprété dans la théorie constructive des types de Martin-Löf. Il est appliqué, d'abord, au français sans symboles mathématiques, avec une attention spéciale aux restrictions...

Un système de règles grammaticales est présenté pour analyser un fragment du français permettant l'expression de théorémes et de preuves mathématiques. Pour cet objectif, on développe une version de la grammaire de Montague, avec des catégories syntaxiques relatives au contexte et aux domaines d'individus. Ce système peut être interprété dans la théorie constructive des types de Martin-Löf. Il est appliqué, d'abord, au français sans symboles mathématiques, avec une attention spéciale aux restrictions...