
doi: 10.1007/bf01182101
The dual discriminator function \(d(x,y,z)\) on a set \(A\) is defined as \(d (a, b, c) = a\) if \(a = b\) and \(d(a,b,c) = c\) if \(a \neq b\). Let \(q(x,y,z)\) be a term of a variety \({\mathcal V}\) of algebras. Then the subvariety \({\mathcal X}\) of \({\mathcal V}\) generated by all algebras in \({\mathcal V}\) where \(q(x,y,z)\) yields the dual discriminator function is called the dual discriminator subvariety of \({\mathcal V}\) defined by \(q(x,y,z)\). A dual discriminator subvariety of \({\mathcal V}\) defined by some term is called a dual discriminator subvariety of \({\mathcal V}\). For example, the variety \({\mathcal L}\) of all lattices contains two dual discriminator subvarieties: the variety \({\mathcal D}\) of distributive lattices and the variety \({\mathcal O}\) consisting of the trivial lattice, only. An algebra \(\langle A; \vee, \wedge \rangle\) is called a weakly associative lattice (WAL), if the two binary operations satisfy the following identities: \[ \begin{aligned} & x \vee x = x = x \wedge x, \\ & x \vee y = y \vee x \text{ and } x \wedge y = y \wedge x, \\ & x \vee (y \wedge x) = x = x \wedge (y \vee x), \\ & x \wedge \bigl[ (x \vee y) \wedge (x \vee z) \bigr] = x = x \vee \bigl[ (x \wedge y) \vee (x \wedge z) \bigr]. \end{aligned} \] Let \({\mathcal W}\) be the variety of all WALs. Since the number of ternary WAL-terms is countable, the number of dual discriminator subvarieties of \({\mathcal W}\) can only be countable. The question is whether this number is finite or infinite. In the paper, infinitely many terms in \({\mathcal W}\) such that they define distinct dual discriminator subvarieties of \({\mathcal W}\) are constructed. As a supplement, a variety \({\mathcal V}\) of WALs which is the union of its dual discriminator subvarieties \({\mathcal V}_0 \subset {\mathcal V}_1 \subset \cdots\) and is not a dual discriminator variety is presented.
Varieties, weakly associative lattice, dual discriminator function, number of dual discriminator subvarieties, Varieties of lattices
Varieties, weakly associative lattice, dual discriminator function, number of dual discriminator subvarieties, Varieties of lattices
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