Tensor products and relation quantales

Abstract

A classical tensor product A ⊗ B of complete lattices A and B, consisting of all down-sets in A × B that are join-closed in either coordinate, is isomorphic to the complete lattice Gal(A, B) of Galois maps from A to B, turning arbitrary joins into meets. We introduce more general kinds of tensor products for closure spaces and for posets. They have the expected universal property for bimorphisms (separately continuous maps or maps preserving restricted joins in the two components) into complete lattices. The appropriate ingredient for quantale constructions is here distributivity at the bottom, a generalization of pseudocomplementedness. We show that the truncated tensor product of a complete lattice B with itself becomes a quantale with the closure of the relation product as multiplication iff B is pseudocomplemented, and the tensor product has a unit element iff B is atomistic. The pseudocomplemented complete lattices form a semicategory in which the hom-set between two objects is their tensor product. The largest subcategory of that semicategory has as objects the atomic boolean complete lattices, which is equivalent to the category of sets and relations. More general results are obtained for closure spaces and posets.

On the Coextension of Cut-Continuous Pomonoids

“…In Section 7, we show that modules over cut-continuous pomonoids admit a tensor product. Here, we take benefit of the notion of a tensor product of closure spaces [9]. In Section 8, we demonstrate that our results may provide a framework for the determination of coextensions of cut-continuous pomonoids.…”

“…Let us first have a look at the order-theoretical aspects. Erné and Picado introduced in [9] the tensor product of arbitrary closure spaces, fulfilling a universal property for mappings from products of closure spaces that are continuous in each argument. Specialised to the present context, where we deal with the closure operator ↑↓ on posets, the situation is as follows.…”