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The Formal Theory of Monads, Univalently

Author Niels van der Weide

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Niels van der Weide
  • Institute for Computing and Information Sciences, Radboud University, Nijmegen, The Netherlands


The author thanks Benedikt Ahrens, Deivid Vale, Herman Geuvers, and Kobe Wullaert for their comments on earlier versions of this paper. The author also thanks the Coq developers for providing the Coq proof assistant and their continuous support to keep compatible with Coq.

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Niels van der Weide. The Formal Theory of Monads, Univalently. In 8th International Conference on Formal Structures for Computation and Deduction (FSCD 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 260, pp. 6:1-6:23, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2023)


We develop the formal theory of monads, as established by Street, in univalent foundations. This allows us to formally reason about various kinds of monads on the right level of abstraction. In particular, we define the bicategory of monads internal to a bicategory, and prove that it is univalent. We also define Eilenberg-Moore objects, and we show that both Eilenberg-Moore categories and Kleisli categories give rise to Eilenberg-Moore objects. Finally, we relate monads and adjunctions in arbitrary bicategories. Our work is formalized in Coq using the library.

Subject Classification

ACM Subject Classification
  • Theory of computation → Logic and verification
  • Theory of computation → Type theory
  • bicategory theory
  • univalent foundations
  • formalization
  • monads
  • Coq


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