lr-Multisemigroups and Modal Convolution Algebras
We show how modal quantales arise as convolution algebras of functions from lr-multisemigroups that is, multisemigroups with a source map l and a target map r, into modal quantales which can be seen as weight or value algebras. In the tradition of boolean algebras with operators we study modal correspondences between algebraic laws in the three algebras. The class of lr-multisemigroups introduced in this article generalises Schweizer and Sklar's function systems and object-free categories to a setting isomorphic to algebras of ternary relations as used in boolean algebras with operators and in substructural logics. Our results provide a generic construction recipe for weighted modal quantales from such multisemigroups. This is illustrated by many examples, ranging from modal algebras of weighted relations as used in fuzzy mathematics, category quantales in the tradition of category algebras or group rings, incidence algebras over partial orders, discrete and continuous weighted path algebras, weighted languages of pomsets with interfaces, and weighted languages associated with presimplicial and precubical sets. We also discuss how these results can be combined with previous ones for concurrent quantales and generalised to a setting that supports reasoning with stochastic matrices or probabilistic predicate transformers.