Regarding arc-wise accessibility in the plane
The existence of a unique solution φ of equation (1) is proved under the condition that f: I → I is convex or concave and of class in I, 0 < f(x) < x in I*, and f’(x) > 0 in I. Here I = [0, a] or [0, a), 0 < a ≤ ∞, and I* = I 0.
The notions of Lipschitz and bilipschitz mappings provide classes of mappings connected to the geometry of metric spaces in certain ways. A notion between these two is given by regular mappings (reviewed in Section 1), in which some non-bilipschitz behavior is allowed, but with limitations on this, and in a quantitative way. In this paper we look at a class of mappings called (s, t)-regular mappings. These mappings are the same as ordinary regular mappings when s = t, but otherwise they behave somewhat...
We discuss differentiability properties of convex functions on Heisenberg groups. We show that the notions of horizontal convexity (h-convexity) and viscosity convexity (v-convexity) are equivalent and that h-convex functions are locally Lipschitz continuous. Finally we exhibit Weierstrass-type h-convex functions which are nowhere differentiable in the vertical direction on a dense set or on a Cantor set of vertical lines.
We study the Hardy-Littlewood maximal operator defined via an unconditional norm, acting on block decreasing functions. We show that the uncentered maximal operator maps block decreasing functions of special bounded variation to functions with integrable distributional derivatives, thus improving their regularity. In the special case of the maximal operator defined by the -norm, that is, by averaging over cubes, the result extends to block decreasing functions of bounded variation, not necessarily...
Článek se snaží přiblížit některé aspekty teorie regulární variace. Jde o pojem z klasické analýzy, který má bohatou historii a četné aplikace v teorii pravděpodobnosti, teorii čísel, integrálních transformacích, komplexní analýze, diferenciálních rovnicích, teorii her či teorii grafů. Regulárně měnící se funkce mají souvislost s mnoha matematickými pojmy, včetně škálové invariance, kterou náš výklad začíná, či konvergenčními testy pro nekonečné řady, kterými náš výklad končí. V průběhu výkladu...
The first section consists of auxiliary results about nondecreasing real functions. In the second section a new characterization of relatively compact sets of regulated functions in the sup-norm topology is brought, and the third section includes, among others, an analogue of Helly's Choice Theorem in the space of regulated functions.