Ergodic and Mixing Probability Measures on [SIN] Groups

We prove that the concepts of completely mixing, mixing, and weakly mixing probability measures on a locally compact group in the class [SIN] are mutually equivalent. A probability measure on such a group is completely mixing if and only if it is ergodic and aperiodic. For measures that are not necessarily aperiodic ergodicity is shown to be equivalent to a mixing-like property which we call almost mixing. Some results on when a probability measure on a [SIN] group is ergodic are also developed. Our methods are based on the theory of boundaries of random walks.     

Quasi-isometries between visual hyperbolic spaces

We prove that a power quasi-symmetric (or PQ-symmetric) homeomorphism between two complete metric spaces can be extended to a quasi-isometry between their hyperbolic approximations. This result can be used to prove that two visual Gromov hyperbolic spaces are quasi-isometric if and only if there is a PQ-symmetric homeomorphism between their boundaries with bounded visual metrics. Also, in the case of trees, we prove that two geodesically complete trees are quasi-isometric if and only if there is a PQ-symmetric homeomorphism between their boundaries with visual metrics based at infinity. We also give a characterization for a map to be PQ-symmetric based on the relative distortion of subsets.     

Jensen measures and analytic multifunctions

This paper describes plurisubharmonic convexity and hulls, and also analytic multifunctions in terms of Jensen measures. In particular, this allows us to get a new proof of Słodkowski's theorem stating that multifunctions are analytic if and only if their graphs are pseudoconcave. We also show that multifunctions with plurisubharmonically convex fibers are analytic if and only if their graphs locally belong to plurisubharmonic hulls of their boundaries. In the last section we prove that minimal analytic multifunctions satisfy the maximum principle and give a criterion for the existence of holomorphic selections in the graphs of analytic multifunctions. The author was partially supported by an NSF Grant.     

Classification of cocycles of generic equivalence relations

We study cocycles of an ergodic generic countable equivalence relation ℜ modulo meager sets. Two cocycles of ℜ are called weakly equivalent if they are cohomologous up to an element of Aut ℜ. It is proved that two nontransient cocycles with values in an arbitrary countable group are weakly equivalent if and only if their generic Mackey actions are isomorphic.     

Elementary Equivalence of Linear Groups Over Rings with a Finite Number of Central Idempotents and Over Boolean Rings

In the present paper, we start with a criterion of elementary equivalence of linear groups over rings with just a finite number of central idempotents. Then we study elementary equivalence of linear groups over Boolean algebras. We prove that two linear groups over Boolean algebras are elementarily equivalent if and only if their dimensions coincide and these Boolean algebras are elementarily equivalent.     

Flow equivalence and orbit equivalence for shifts of finite type and isomorphism of their groupoids

We give conditions for when continuous orbit equivalence of one-sided shift spaces implies flow equivalence of the associated two-sided shift spaces. Using groupoid techniques, we prove that this is always the case for shifts of finite type. This generalises a result of Matsumoto and Matui from the irreducible to the general case. We also prove that a pair of one-sided shift spaces of finite type are continuously orbit equivalent if and only if their groupoids are isomorphic, and that the corresponding two-sided shifts are flow equivalent if and only if the groupoids are stably isomorphic. As applications we show that two finite directed graphs with no sinks and no sources are move equivalent if and only if the corresponding graph $C^{?}$-algebras are stably isomorphic by a diagonal-preserving isomorphism (if and only if the corresponding Leavitt path algebras are stably isomorphic by a diagonal-preserving isomorphism), and that two topological Markov chains are flow equivalent if and only if there is a diagonal-preserving isomorphism between the stabilisations of the corresponding Cuntz–Krieger algebras (the latter generalises a result of Matsumoto and Matui about irreducible topological Markov chains with no isolated points to a result about general topological Markov chains). We also show that for general shift spaces, strongly continuous orbit equivalence implies two-sided conjugacy.     

Weak Equivalence of Internal Categories

Weak equivalence is defined as equivalence in the bicategory of modules between internal categories. It is known that two categories are weakly equivalent if and only if their Cauchy completions are equivalent. We prove that this condition can be generalized to a suitable notion of intermediate category, stable under composition with weak equivalences. Applications to categorical Morita theory are given.     

Universal theories for partially commutative metabelian groups

We look at properties of partially commutative metabelian groups and of their universal theories. In particular, it is shown that two partially commutative metabelian groups defined by cycles are universally equivalent if and only if the cycles are isomorphic.     

Two remarks on the first-order theories of Baumslag-Solitar groups

We characterize all finitely generated groups elementarily equivalent to a solvable Baumslag-Solitar group BS(m, 1). It turns out that a finitely generated group G is elementarily equivalent to BS(m, 1) if and only if G is isomorphic to BS(m, 1). Furthermore, we show that two Baumslag-Solitar groups are existentially (universally) equivalent if and only if they are elementarily equivalent if and only if they are isomorphic.     

Strong Morita equivalence for ordered semigroups with local units

We prove that partially ordered semigroups with local units are strongly Morita equivalent if and only if they have a joint enlargement, which in turn happens if and only if the Cauchy completions of the semigroups are equivalent.     

A Complete Solution to the Chromatic Equivalence Class of Graph B_(n-8,1,4)

Two graphs are defined to be adjointly equivalent if and only if their complements are chromatically equivalent.Using the properties of the adjoint polynomials and the fourth character R_4(G),the adjoint equivalence class of graph B_(n-8,1,4) is determined.According to the relations between adjoint polynomial and chromatic polynomial,we also simultaneously determine the chromatic equivalence class of B_(n-8,1,4) that is the complement of B_(n-8,1,4).     

Code and order in polygonal billiards

Two polygons P, Q are code equivalent if there are billiard orbits u, v which hit the same sequence of sides and such that the projections of the orbits are dense in the boundaries ∂P, ∂Q. Our main results show when code equivalent polygons have the same angles, resp. are similar, resp. affinely similar.     

Decomposable compositions, symmetric quasisymmetric functions and equality of ribbon Schur functions

We define an equivalence relation on integer compositions and show that two ribbon Schur functions are identical if and only if their defining compositions are equivalent in this sense. This equivalence is completely determined by means of a factorization for compositions: equivalent compositions have factorizations that differ only by reversing some of the terms. As an application, we can derive identities on certain Littlewood-Richardson coefficients.Finally, we consider the cone of symmetric functions having a nonnnegative representation in terms of the fundamental quasisymmetric basis. We show the Schur functions are among the extremes of this cone and conjecture its facets are in bijection with the equivalence classes of compositions.     

完全解决图$\overline{B_{n-8,1,4}}$的色等价类

Two graphs are defined to be adjointly equivalent if and only if their complements are chromatically equivalent.Using the properties of the adjoint polynomials and the fourth character R₄（G）,the adjoint equivalence class of graph B_n-8,1,4 is determined.According to the relations between adjoint polynomial and chromatic polynomial,we also simultaneously determine the chromatic equivalence class of B_n-8,1,4 that is the complement of B_n-8,1,4.     

Morita equivalence and Pedersen ideals

We show that two -algebras are strongly Morita equivalent if and only if their Pedersen ideals are Morita equivalent as rings with involution.

     

Cancellation law for homoiopy equivalent representations of groups op odd order

We prove that if V and W are real G-modules and G is a group of odd order, then V and W are stably G-homotopy equivalent if and only if they are G-homotopy equivalent.     

由格蕴涵代数诱导的伴随半群

给出由格蕴涵代数诱导出的伴随半群及有关概念 ,详细讨论伴随半群中的元素即格蕴涵代数的左映射的性质 ,得到它们的几个等价条件。最后讨论由格蕴涵代数诱导的两个双格半群与伴随半群之间的关系 ,并证明这些半群是幂等的当且仅当它们是由格 H蕴涵代数所诱导     

Various Structures Associated to the Representation Categories of Eight-Dimensional Nonsemisimple Hopf Algebras

We determine various additional structures on all nonsemisimple Hopf algebras of dimension 8 over an algebraically closed field k of characteristic 0, including their representation rings and quasitriangular structures. As a consequence, it is shown that for two such Hopf algebras, the tensor categories of their representations are monoidally equivalent if and only if the representation rings of them are isomorphic as rings. An erratum to this article is available at .     

Cochains and homotopy type

Finite type nilpotent spaces are weakly equivalent if and only if their singular cochains are quasi-isomorphic as E_∞ algebras. The cochain functor from the homotopy category of finite type nilpotent spaces to the homotopy category of E_∞ algebras is faithful but not full.