A Tour on Ecumenical Systems (Invited Talk)

Authors Elaine Pimentel , Luiz Carlos Pereira

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Elaine Pimentel
  • Department of Computer Science, University College London, UK
Luiz Carlos Pereira
  • Department of Philosophy, UERJ, Brazil


We want to thank Dag Prawitz for the friendship and inspiration, and our co-authors in this endeavour: Valeria de Paiva, Sonia Marin, Emerson Sales, Delia Kesner, Mariana Milicich, Victor Nascimento and Carlos Olarte.

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Elaine Pimentel and Luiz Carlos Pereira. A Tour on Ecumenical Systems (Invited Talk). In 10th Conference on Algebra and Coalgebra in Computer Science (CALCO 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 270, pp. 3:1-3:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


Ecumenism can be understood as a pursuit of unity, where diverse thoughts, ideas, or points of view coexist harmoniously. In logic, ecumenical systems refer, in a broad sense, to proof systems for combining logics. One captivating area of research over the past few decades has been the exploration of seamlessly merging classical and intuitionistic connectives, allowing them to coexist peacefully. In this paper, we will embark on a journey through ecumenical systems, drawing inspiration from Prawitz' seminal work [Dag Prawitz, 2015]. We will begin by elucidating Prawitz' concept of "ecumenism" and present a pure sequent calculus version of his system. Building upon this foundation, we will expand our discussion to incorporate alethic modalities, leveraging Simpson’s meta-logical characterization. This will enable us to propose several proof systems for ecumenical modal logics. We will conclude our tour with some discussion towards a term calculus proposal for the implicational propositional fragment of the ecumenical logic, the quest of automation using a framework based in rewriting logic, and an ecumenical view of proof-theoretic semantics.

Subject Classification

ACM Subject Classification
  • Theory of computation → Proof theory
  • Theory of computation → Modal and temporal logics
  • Theory of computation → Logic and verification
  • Theory of computation → Type theory
  • Intuitionistic logic
  • classical logic
  • modal logic
  • ecumenical systems
  • proof theory


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