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Monoidal Company for Accessible Functors Basold, Henning Pous, Damien Rot, Jurriaan coalgebras distributive laws accessible functors monoidal categories Distributive laws between functors are a fundamental tool in the theory of coalgebras. In the context of coinduction in complete lattices, they correspond to the so-called compatible functions, which enable enhancements of the coinductive proof technique. Amongst these, the greatest compatible function, called the companion, has recently been shown to satisfy many good properties. Categorically, the companion of a functor corresponds to the final object in a category of distributive laws. We show that every accessible functor on a locally presentable category has a companion. Central to this and other constructions in the paper is the presentation of distributive laws as coalgebras for a certain functor. This functor itself has again, what we call, a second-order companion. We show how this companion interacts with the various monoidal structures on functor categories. In particular, both the first- and second-order companion give rise to monads. We use these results to obtain an abstract GSOS-like extension result for specifications involving the second-order companion. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Henning Basold and Damien Pous and Jurriaan Rot 2017 Is Part Of LIPIcs, Volume 72, 7th Conference on Algebra and Coalgebra in Computer Science (CALCO 2017) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.CALCO.2017.5 urn:nbn:de:0030-drops-80379 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CALCO.2017.5 eng https://creativecommons.org/licenses/by/3.0/legalcode