Restriction semigroups model algebras of partial maps under composition and domain.
Here we consider restriction semigroups for which the usual Boolean operations on …

In this article we establish the undecidability of representability and of finite representability
as algebras of binary relations in a wide range of signatures. In particular, representability …

The" if–then–else" construction is one of the most elementary programming commands, and
its abstract laws have been widely studied, starting with McCarthy. Possibly, the most …

We show that strict deterministic propositional dynamic logic with intersection is highly
undecidable, solving a problem in the Stanford Encyclopedia of Philosophy. In fact we show …

We examine the problem of representing semigroups as binary relations, partial maps and
injective functions, with the constraint that certain pre-designated idempotent elements must …

We characterize algebras of transformations on a set under the operations of composition
and the pointwise switching function defined as follows:(f, g)[h, k](x)= h (x) if f (x)= g (x), and k …

Two propositions may be regarded as doxastically equivalent if revision of an agent's beliefs
to adopt either has the same effect on the agent's belief state. We enrich the language of …

We establish the undecidability of representability and of finite representability as algebras
of binary relations in a wide range of signatures. In particular, representability and finite …

Numerous authors have given complete descriptions of those varieties whose members
have all congruences determined by the congruence class containing a given nullary …

Abstract In any 0-normal variety (0-regular variety in which {0} is a subalgebra), every
congruence class containing 0 is a subalgebra. These “normal subalgebras” of a fixed …