Model categories were introduced by Quillen [Q] to provide a framework through which one could apply homotopy theory in various settings. They have been astonishingly successful in this regard, and in recent years one of the first things one does when studying any homotopical situation is to try to set up a model structure. The aim of this paper is to introduce a new, but very basic, tool into ...

following the categorical approach to universal algebra through algebraic theories, proposed by f.~w.~lawvere in his phd thesis, this paper aims at introducing a similar setting for general topology. the cornerstone of the new framework is the notion of emph{categorically-algebraic} (emph{catalg}) emph{topological theory}, whose models induce a category of topological structures. we introduce t...

Following the categorical approach to universal algebra through algebraic theories, proposed by F.~W.~Lawvere in his PhD thesis, this paper aims at introducing a similar setting for general topology. The cornerstone of the new framework is the notion of emph{categorically-algebraic} (emph{catalg}) emph{topological theory}, whose models induce a category of topological structures. We introduce t...

Though unifications of some of the numerous theories of default reasoning have been found, we add to doubts about the existence of universal theories by viewing default reasoning from the standpoint of decision theory as a case of rational self-government of inference. Default rules express not only methods for deriving new conclusions from old, but also preferences among sets of possible concl...

A notion called Herbrand saturation is shown to provide the modeltheoretic analogue of a proof-theoretic method, Herbrand analysis, yielding uniform model-theoretic proofs of a number of important conservation theorems. A constructive, algebraic variation of the method is described, providing yet a third approach, which is finitary but retains the semantic flavor of the model-theoretic version.

nowdays, democracy is become an universal value so that all intellectual tendencies should put it into their concerns. whether it accepts or not? the central value is caused a change in many political theories to democracy. it seems that one of most important these endeavors is concerned to practitioners of political philosophy that have attempted to revise negative attitudes of it. this articl...