(1) Elkan’s proof uses too strong a notion of logical equivalence. The particular equivalence he considers, while valid in Boolean algebra, has nothing to do with fuzzy logic. (2) Elkan claims that De Morgan’s algebra “allows very little reasoning about collections of fuzzy assertions,” although he correctly states that when logical equivalence is restricted to De Morgan algebra equalities’ “co...

We prove that the topology of a compact Hausdorff topological Heyting algebra is a Stone topology. It then follows from known results that a Heyting algebra is profinite iff it admits a compact Hausdorff topology that makes it a compact Hausdorff topological Heyting algebra.

In this paper, we begin to study the subalgebra lattice of a Leibniz algebra. particular, deal with algebras whose is modular, upper semi-modular, lower distributive, or dually atomistic. The fact that non-Lie algebra has fewer one-dimensional subalgebras in general results number conditions being weaker than Lie case.

In this note we show that every de Morgan algebra is isomorphic to a two-subset algebra, 〈P,⊔,⊓,∼, 0P , 1P 〉, where P is a set of pairs (X,Y ) of subsets of a set I, (X,Y )⊔(X , Y ) = (X∩X , Y ∪Y ), (X,Y )⊓(X , Y ) = (X ∪ X , Y ∩ Y ), ∼ (X,Y ) = (Y,X), 1P = (∅, I), and 0P = (I, ∅). This characterization generalizes a previous result that applied only to a special type of de Morgan algebras call...

We investigate a generalization of Hopf algebra slq (2) by weakening the invertibility of the generator K, i.e. exchanging its invertibility KK = 1 to the regularity KKK = K. This leads to a weak Hopf algebra wslq (2) and a J-weak Hopf algebra vslq (2) which are studied in detail. It is shown that the monoids of group-like elements of wslq (2) and vslq (2) are regular monoids, which supports th...

Hamkins and Löwe proved that the modal logic of forcing is S4.2. In this paper, we consider its modal companion, the intermediate logic KC and relate it to the fatal Heyting algebra HZFC of forcing persistent sentences. This Heyting algebra is equationally generic for the class of fatal Heyting algebras. Motivated by these results, we further analyse the class of fatal Heyting algebras.

In this paper we study the structure of finitely presented Heyting algebras. Using algebraic techniques (as opposed to techniques from proof-theory) we show that every such Heyting algebra is in fact coHeyting, improving on a result of Ghilardi who showed that Heyting algebras free on a finite set of generators are co-Heyting. Along the way we give a new and simple proof of the finite model pro...