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Relation lifting, with an application to the many-valued cover modality

Marta Bilkova ; Alexander Kurz ; Daniela Petrisan ; Jiri Velebil.

We introduce basic notions and results about relation liftings on categories enriched in a commutative quantale. We derive two necessary and sufficient conditions for a 2-functor T to admit a functorial relation lifting: one is the existence of a distributive law of T over the "powerset monad" on&nbsp;[&hellip;]

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Semantics of Higher-Order Recursion Schemes

Jiri Adamek ; Stefan Milius ; Jiri Velebil.

Higher-order recursion schemes are recursive equations defining new operations from given ones called "terminals". Every such recursion scheme is proved to have a least interpreted semantics in every Scott's model of \lambda-calculus in which the terminals are interpreted as continuous operations.&nbsp;[&hellip;]

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Positive fragments of coalgebraic logics

Adriana Balan ; Alexander Kurz ; Jiří Velebil.

Positive modal logic was introduced in an influential 1995 paper of Dunn as the positive fragment of standard modal logic. His completeness result consists of an axiomatization that derives all modal formulas that are valid on all Kripke frames and are built only from atomic propositions,&nbsp;[&hellip;]

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Elgot Algebras

Jiri Adamek ; Stefan Milius ; Jiri Velebil.

Denotational semantics can be based on algebras with additional structure (order, metric, etc.) which makes it possible to interpret recursive specifications. It was the idea of Elgot to base denotational semantics on iterative theories instead, i.e., theories in which abstract recursive&nbsp;[&hellip;]

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Extending set functors to generalised metric spaces

Adriana Balan ; Alexander Kurz ; Jiří Velebil.

For a commutative quantale $\mathcal{V}$, the category $\mathcal{V}-cat$ can be perceived as a category of generalised metric spaces and non-expanding maps. We show that any type constructor $T$ (formalised as an endofunctor on sets) can be extended in a canonical way to a type constructor&nbsp;[&hellip;]

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