Prefijos y sufijos en el proyectar de la arquitectura

La relación entre la formación de las palabras y las oraciones con la de los edificio

Tree Deletion Set has a Polynomial Kernel (but no OPT^O(1) approximation)

In the Tree Deletion Set problem the input is a graph G together with an integer k. The objective is to determine whether there exists a set S of at most k vertices such that G-S is a tree. The problem is NP-complete and even NP-hard to approximate within any factor of OPT^c for any constant c. In this paper we give a O(k^4) size kernel for the Tree Deletion Set problem. To the best of our knowledge our result is the first counterexample to the "conventional wisdom" that kernelization algorithms automatically provide approximation algorithms with approximation ratio close to the size of the kernel. An appealing feature of our kernelization algorithm is a new algebraic reduction rule that we use to handle the instances on which Tree Deletion Set is hard to approximate

A red-figure calyx-krater from Troizen

A fragmentary red-figure calyx-krater was found in a salvage excavation at the area of Troizen’s eastern cemetery. Hephaistos returning to Olympos on muleback, accompanied by Dionysos and members of his thiasos, is depicted on the surviving part of the body. The configuration of the scene and the drawing style point to the workshop of the Pronomos Painter, active in the late 5th and early 4th centuries BC. The vase was most probably fashioned shortly after the beginning of the 4th century, as is indicated by specific features in its shape. The scene belongs among the few late depictions of Hephaistos’ Return in Attic vase painting, as the great majority of other known examples date from the 6th and 5th centuries BC. The representation follows the norms of the established iconography of the subject, while also exhibiting some innovative features: the figures are set at various levels, an arrangement creating the illusion of depth and perhaps reflecting influences from monumental painting; Hephaistos and Dionysos are portrayed as nude beardless youths, whereas in earlier or contemporary representations of this subject matter they are normally draped and bearded; a Nike flying above Dionysos and lending the procession a triumphant character appears for the first time in this scene