In this article a sequential theory in the category of spaces and proper maps is described and developed. As a natural extension a sequential theory for exterior spaces and maps is obtained.
The Vietoris monad on the category of compact Hausdorff spaces is a topological analogue of the power-set monad on the category of sets. Exploiting Manes characterisation of the compact Hausdorff spaces as algebras for the ultrafilter monad on sets,
we give precise form to the above analogy by exhibiting the Vietoris monad as induced by a weak distributive law, in the sense of Bohm, of the power-set monad over the ultrafilter monad.
Internal preneighbourhood spaces were first conceived inside any finitely complete category with finite coproducts and proper factorisation structure in my earlier paper. In this paper a closure operation is introduced on internal preneighbourhood sp
aces and investigated along with closed morphisms and its close allies. Analogues of several well known classes of topological spaces for preneighbourhood spaces are investigated. The approach via preneighbourhood systems is shown to be more general than the closure operators and conveniently allows to identify properties of classes of morphisms which are independent of continuity of morphisms with respect to closure operators.
Under a general categorical procedure for the extension of dual equivalences as presented in this papers predecessor, a new algebraically defined category is established that is dually equivalent to the category $bf LKHaus$ of locally compact Hausdor
ff spaces and continuous maps, with the dual equivalence extending a Stone-type duality for the category of extremally disconnected locally compact Hausdorff spaces and continuous maps. The new category is then shown to be isomorphic to the category $bf CLCA$ of complete local contact algebras and suitable morphisms. Thereby, a new proof is presented for the equivalence ${bf LKHaus}simeq{bf CLCA}^{rm op}$ that was obtained by the first author more than a decade ago. Unlike the morphisms of $bf CLCA$, the morphisms of the new category and their composition law are very natural and easy to handle.
Given a continuous monadic functor T in the category of Tychonov spaces for each discrete topological semigroup X we extend the semigroup operation of X to a right-topological semigroup operation on TX whose topological center contains the dense subs
emigroup of all elements of TX that have finite support.
The $pi$ -calculus is used as a model for programminglanguages. Its contexts exhibit arbitrary concurrency, makingthem very discriminating. This may prevent validating desir-able behavioural equivalences in cases when more disciplinedcontexts are exp
ected.In this paper we focus on two such common disciplines:sequentiality, meaning that at any time there is a single threadof computation, and well-bracketing, meaning that calls toexternal services obey a stack-like discipline. We formalise thedisciplines by means of type systems. The main focus of thepaper is on studying the consequence of the disciplines onbehavioural equivalence. We define and study labelled bisim-ilarities for sequentiality and well-bracketing. These relationsare coarser than ordinary bisimilarity. We prove that they aresound for the respective (contextual) barbed equivalence, andalso complete under a certain technical condition.We show the usefulness of our techniques on a number ofexamples, that have mainly to do with the representation offunctions and store.