Topological finite-determinacy of functions with non-isolated singularities

We introduce the concept of topological finite-determinacy for germs of analytic functions within a fixed ideal I, which provides a notion of topological finite-determinacy of functions with non-isolated singularities. We prove the following statement which generalizes classical results of Thom and Varchenko: let A be the complement in the ideal I of the space of germs whose topological type remains unchanged under a deformation within the ideal that only modifies sufficiently large order terms of the Taylor expansion. Then A has infinite codimension in I in a suitable sense. We also prove the existence of generic topological types of families of germs of I parametrized by an irreducible analytic set.     

Sur les notions de quasi-homogénéité de feuilletages holomorphes endimension deux

In this note, we recall the different notions of quasi-homogeneity for singular germs of holomorphic foliations in the plane presented in [6]. The classical notion of quasi-homogenity allude to those functions which belong to its own jacobian ideal. Given a foliation in the plane, asking that the equation of the separatrix set is a classical quasi-homogeneous function we obtain a natural generalization in the context of foliations. On the other hand, topological quasi-homogeneity is characterized by the fact that every topologically trivial deformation whose sepatrix family is analytically trivial is an analytically trivial deformation. We give an explicit example of a topological quasi-homogeneous foliation which is not quasi-homogeneous in the sense given above.

     

Algebraic and topological closure conditions for classes of pseudo-Boolean functions

We examine classes of real-valued functions of 0-1 variables closed under algebraic operations as well as topological convergence, and having a certain local characteristic (requiring that any function not in the class should have a k-variable minor not belonging to this class). It is shown that for k=2, the only 4 maximal classes with these properties are those of submodular, supermodular, monotone increasing and monotone decreasing functions. All the 13 locally defined closed classes are determined and shown to be intersections of the 4 maximal ones. All maximal classes for k≥3 are determined and characterized by the sign of higher order derivatives of the functions in the class.     

A universal complex structure on complete metrizable topological spaces

Let X be a topological space whose topology may be defined by a complete metric d. Taking all such metrics d we define a universal complex structure on X. For this complex structure the sheaf of germs of holomorphic functions on X coincides with the sheaf of germs of continuous functions on X, and hence the theories of topological and holomorphic vector bundles on X are the same.     

Classes de conjugaison des flots du plan topologiquement équivalents au flot de Reeb

We describe the conjugacy classes of topological flows in the plane whose orbits are the leaves of the Reeb foliation, using an invariant which takes its values in the quotient space of an equivalence relation on germs of numerical functions.     

Topologies on the subgroup lattice of a compact group

Let G be a compact topological group. The lattice ΣG of its closed subgroups is algebraic in the reversed order, hence is made a compact topological semilattice by its dual Lawson topology. A second natural order-compatible compact topology on ΣG arises from the usual topology on the set of closed subsets of G. These topologies are shown to coincide precisely if the identity component is central in G, but to be essentially different otherwise, since they also fail to satisfy natural weakenings of the equality condition. In the second part of the paper the groups G are determined in which one of the lattice operations of ΣG becomes continuous with respect to either one of these topologies; several different characterizations of these cases are also provided.     

The Denef-Loeser Zeta Function is not a Topological Invariant

An example is given which shows that the Denef–Loeserzeta function (usually called the topological zeta function)associated to a germ of a complex hypersurface singularity isnot a topological invariant of the singularity. The idea isthe following. Consider two germs of plane curves singularitieswith the same integral Seifert form but with different topologicaltype and which have different topological zeta functions. Makea double suspension of these singularities (consider them ina 4-dimensional complex space). A theorem of M. Kervaire andJ. Levine states that the topological type of these new hypersurfacesingularities is characterized by their integral Seifert form.Moreover the Seifert form of a suspension is equal (up to sign)to the original Seifert form. Hence these new singularitieshave the same topological type. By means of a double suspensionformula the Denef–Loeser zeta functions are computed forthe two 3-dimensional singularities and it is verified thatthey are not equal.     

The closed subalgebras of a topological algebra

Conclusion There are some interesting related problems which we have not solved One is to characterize the family of all closed subalgebras in the case where it is assumed that the algebraic operations are continuous in the topology. If the operations are not determined uniquely by the family of closed subalgebras, is there at least one determination in which they are continuous ? Another problem is to characterize the families of finitely generated closed subalgebras of a topological algebra.Supported by National Science Foundation Research Grant GP-3132.     

Infinite distributive laws versus local connectedness and compactness properties

Various local connectedness and compactness properties of topological spaces are characterized by higher degrees of distributivity for their lattices of open (or closed) sets, and conversely. For example, those topological spaces for which not only the lattice of open sets but also that of closed sets is a frame, are described by the existence of web neighborhood bases, where webs are certain specific path-connected sets. Such spaces are called web spaces. The even better linked wide web spaces are characterized by F-distributivity of their topologies, and the worldwide web spaces (or C-spaces) by complete distributivity of their topologies. Similarly, strongly locally connected spaces and locally hypercompact spaces are characterized by suitable infinite distributive laws. The web space concepts are also viewed as natural extensions of spaces that are semilattices with respect to the specialization order and have continuous (unary, binary or infinitary) semilattice operations.     

A class of strong forms of fuzzy complete continuity

The aim of this paper is devoted to make use of operations on I^X of a fuzzy topological space X to unify and generalize classes of strong forms of fuzzy complete continuity. Furthermore, we add more types of strong forms of fuzzy completely continuous functions by choosing special operations. A comparison between these types of functions is of interest. Preservations of some fuzzy aspects under these functions are studied.     

CARTESIAN CLOSED COREFLECTIVE HULLS

Conditions are established under which a given class of objects in a topological category will have a Cartesian closed coreflective hull. The main theorem is used to discover new Cartesian closed topological categories and to unify a diversity of known special results. It also provides a mild criterion for the existence of Cartesian closed topological hulls.     

Universal topological algebra needs closed topological categories

It is shown that a development of universal topological algebra, based in the obvious way on the category of topological spaces, leads in general to a pathological situation. The pathology disappears when the base category is changed to a cartesian closed topological category or to a topological category endowed with a compatible closed symmetric monoidal structure, provided that in the latter case, the algebraic operations are expressed in terms of monoidal powers rather than the usual cartesian powers. With such base categories, universal topological algebra becomes virtually as well-behaved as ordinary (setbased) universal algebra.     

Closed classes of functions, generalized constraints, and clusters

Classes of functions of several variables on arbitrary nonempty domains that are closed under permutation of variables and addition of dummy variables are characterized by generalized constraints, and hereby Hellerstein’s Galois theory of functions and generalized constraints is extended to infinite domains. Furthermore, classes of operations on arbitrary nonempty domains that are closed under permutation of variables, addition of dummy variables, and composition are characterized by clusters, and a Galois connection is established between operations and clusters.     

Some results on quasipolyhedral convexity

The objective of this paper is to analyze under what well-known operations the class of quasipolyhedral convex functions, which can be regarded as an extension of that of polyhedral convex functions, is closed. The operations that will be considered are those that preserve polyhedral convexity, such that the image and the inverse image under linear transformations, right scalar multiplication (including the case where λ=0⁺) and pointwise addition.      

A topological structure on a set of continous functions with various domains

We construct a topological space of continuous functions which generalizes the previously studied space of functions defined on closed intervals. For the new space, metrizability properties are studied. The results can be applied in the topological theory of ordinary differential equations. Translated fromMatematicheskie Zametki, Vol. 66, No. 1, pp. 76–88, July, 1999.     

Some properties of algebras of real-valued measurable functions

Measures and measurable functions are used primarily as tools for carrying out various calculations to increase our knowledge. We learn how to combine them in various ways by studying real analysis; a very useful subject on which very much has been written. In this paper, we regard measurable functions as algebras of real-valued functions (or equivalence classes of them) on a set or topological space under point-wise addition, multiplication, or lattice operations and our techniques resemble closely those used to study algebras of continuous functions. This is done by examining a number of explicit examples including Borel and Lebesgue measures and measurable functions.     

Local times of stochastic processes with positive definite bivariate densities

A new class of stochastic processes, called processes of positive bivariate type, is defined. Such a process is typically one whose bivariate density functions are positive definite, at least for pairs of time points which are sufficiently mutually close. The class includes stationary Gaussian processes and stationary reversible Markov processes, and is closed under the operations of composition and convolution. The purpose of this work is to show that the local times of such processes can be investigated in a natural way. One of the main contributions is an orthogonal expansion of the local time which is new even in the well-studied stationary Gaussian case. The basic tool in its construction is the Lancaster-Sarmanov expansion of a bivariate density in a series of canonical correlations and canonical variables.     

Local semianalytic geometry

This paper treats the theory of semianalytic function germs over real closed fields more general than . An ordered field is microbial if it has a non-zero element whose powers converge to zero. The fields we treat are direct limits of countable microbial subfields. We define local rings of analytic function germs algebraically and use the Weierstrass preparation theory to prove an Artin-Lang property. We end by relating seminash functions to abstract semialgebraic functions on the real spectrum of the local rings.     

Topological Complexity of Zero-Finding

The topological complexity of zero-finding is studied using a BSS machine over the reals with an information node. The topological complexity depends on the class of functions, the class of arithmetic operations, and on the error criterion. For the root error criterion the following results are established. If only Hölder operations are permitted as arithmetic operations then the topological complexity is roughly −log₂ε and bisection is optimal. This holds even for the small class of linear functions. On the other hand, for the class of all increasing functions, if we allow the sign function or division, together with log and exp, then the topological complexity drops to zero. For the residual error criterion, results can be totally different than for the root error criterion. For example, the topological complexity can be zero for the residual error criterion, and roughly −log₂ε for the root error criterion.     

EXPONENTIAL LAW AND θ-CONTINUOUS FUNCTIONS

Abstract

The category θ-Top of topological spaces and θ-continuous functions is not Cartesian closed; but it is known that under certain local property assumptions, the exponential law in θ-Top is fulfilled. We define a functor from θ-Top to the category of H-θ-topological spaces and prove that in this category the exponential law holds without any local property assumptions. We also provide a functor from θ-Top to Katětov's category of filter-merotopic spaces, which is Cartesian closed.