Masasi Higasikawa
We investigate some properties of topological groups related to disconnectedness or Archimedeanness. We prove or disprove the preservation of those under operations as subgroups, quotients, products, etc. Characterizations of non-Archimedeanness are obtained by using embedding into universal groups. We also clarify the differences between the properties by constructing miscellaneous Polish groups.
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Topological groups whose underlying spaces are basically disconnected, $F$-, or $F'$-spaces but not $P$-spaces are considered. It is proved, in particular, that the existence of a Lindelöf basically disconnected topological group which is not a $P$-space is equivalent to the existence of a Boolean basically disconnected Lindelöf group of countable pseudocharacter, that free and free Abelian topological groups of zero-dimensional non-$P$-spaces are never $F'$-spaces, and that the existence of a free Boolean $F'$-group which is not a $P$-space is equivalent to that of selective ultrafilters on $…
This is a survey of some of the consequences of the recently introduced congruences on the theory of connectednesses (radical classes) and disconnectednesses (semisimple classes) of graphs and topological spaces. In particular, it is shown that the connectednesses and disconnectednesses can be obtained as Hoehnke radicals and a connectedness has a characterization in terms of congruences resembling the classical characterization of its algebraic counterpart using ideals for a radical class. But this approach has also shown that there are some unexpected differences and surprises: an ideal-here…
Disconnectedness and unboundedness of the solution sets of monotone vector variational inequalities
本文研究单调向量变分不等式解集的拓扑结构，证明弱Pareto解集和proper Pareto解集若不连通则每个连通分量必无界，并提出两个开放问题。
We denote by C_p(X,G) the group of all continuous functions from a space X to a topological group G endowed with the topology of pointwise convergence. We say that spaces X and Y are G-equivalent provided that the topological groups C_p(X,G) and C_p(Y,G) are topologically isomorphic. We investigate which topological properties are preserved by G-equivalence, with a special emphasis being placed on characterizing topological properties of X in terms of those of C_p(X,G). Since R-equivalence coincides with l-equivalence, this line of research "includes" major topics of the classical C_p-theory o…
This collection of thirty two reviewed articles covers several fields of General Topology. Several contributions represent invited presentations at the Ninth Prague Topological Symposium.
Super calibers in topological spaces and topological hyperspaces
本文研究拓扑空间及其超空间的超口径概念，统一已知结果，刻画无限可度量化空间中超口径差异情形，并证明一个ZFC独立性结果。
We show that the following properties are preserved under inverse limits: countable fan-tightness, q+, discrete generation and selective separability. We also present several examples based on inverse limits of countable spaces.
Several mathematicians, including myself, have studied some unifications in general topological spaces as well as in fuzzy topological spaces. For instance in our earlier works, using operations on topological spaces, we have tried to unify some concepts similar to continuity, openness, closedness of functions, compactness, filter convergence, closedness of graphs, countable compactness and Lindelof property. In this article, to obtain further unifications, we will study $ϕ_{1,2}$-compactness and relations between $ϕ_{1,2}$-compactness, filters and $ϕ_{1,2}$% -closure operator.
We investigate whether an arbitrary base for a dense-in-itself topological space can be partitioned into two bases. We prove that every base for a T_3 Lindelöf topology can be partitioned into two bases while there exists a consistent example of a first countable, 0-dimensional, Hausdorff space of size continuum and weight ω_1 which admits a point countable base without a partition to two bases. Several related results are proved and the paper finishes with a list of open problems.
We present several known and new results on the Baire category properties in topological groups. In particular, we prove that a Baire topological group $X$ is metrizable if and only if $X$ is point-cosmic if and only if $X$ is a $σ$-space. A topological group $X$ is Choquet if and only if its Raikov completion $\bar X$ is Choquet and $X$ is $G_δ$-dense in $\bar X$. A topological group $X$ is complete-metrizable if and only if $X$ is a point-cosmic Choquet space if and only if $X$ is a Choquet $σ$-space. Finally, we pose several open problem, in particular, if each Choquet topological group is …
We give a "limit-free formula" simplifying the computation of the topological entropy for topological automorphisms of totally disconnected locally compact groups. This result allows us to extend several basic properties of the topological entropy known to hold for compact groups.
A note on asymptotic behaviors and topological properties of two smooth real-valued functions and several graphs associated to them
本文研究两个无交点的光滑实值函数在平面中的图及其拓扑性质，探讨Reeb空间的构造与性质，总结其在Morse函数理论中的应用。
Some notes on Pontryagin duality of abelian topological groups
本文探讨了阿贝尔pro-Lie群中Pontryagin对偶性相关的若干问题，分析了该领域内的核心方法与主要贡献。
Locally solid Riesz spaces have been widely investigated in the past several decades; but locally solid topological lattice-ordered groups seem to be largely unexplored. The paper is an attempt to initiate a relatively systematic study of locally solid topological lattice-ordered groups. We give both Robert-Namioka-type characterization and Fremlin-type characterization of locally solid topological lattice-ordered groups. In particular, we show that a group topology on a lattice-ordered group is locally solid if and only if it is generated by a family of translation-invariant lattice pseudomet…
The notion of entropy appears in many fields and this paper is a survey about entropies in several branches of Mathematics. We are mainly concerned with the topological and the algebraic entropy in the context of continuous endomorphisms of locally compact groups, paying special attention to the case of compact and discrete groups respectively. The basic properties of these entropies, as well as many examples, are recalled. Also new entropy functions are proposed, as well as generalizations of several known definitions and results. Furthermore we give some connections with other topics in Math…
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