Indexed induction and coinduction, fibrationally.

Neil Ghani, Patricia Johann, Clement Fumex

Research output: Chapter in Book/Report/Conference proceedingConference contribution book

11 Citations (Scopus)
130 Downloads (Pure)


This paper extends the fibrational approach to induction and coinduction pioneered by Hermida and Jacobs, and developed by the current authors, in two key directions. First, we present a sound coinduction rule for any data type arising as the final coalgebra of a functor, thus relaxing Hermida and Jacobs’ restriction to polynomial data types. For this we introduce the notion of a quotient category with equality (QCE), which both abstracts the standard notion of a fibration of relations constructed from a given fibration, and plays a role in the theory of coinduction dual to that of a comprehension category with unit (CCU) in the theory of induction. Second, we show that indexed inductive and coinductive types also admit sound induction and coinduction rules. Indexed data types often arise as initial algebras and final coalgebras of functors on slice categories, so our key technical results give sufficent conditions under which we can construct, from a CCU (QCE) U : E -> B, a fibration with base B/I that models indexing by I and is also a CCU (QCE).
Original languageEnglish
Title of host publicationAlgebra and coalgebra in computer science
Subtitle of host publicationProceedings of the 4th international conference, CALCO 2011, Winchester, UK, August 30 - September 2, 2011
EditorsAndrea Corradini, Bartek Klin, Corina Cirstea
Number of pages15
ISBN (Print)9783642229435
Publication statusPublished - 2011

Publication series

NameLecture Notes in Computer Science
ISSN (Print)0302-9743


  • automata theory
  • reversible processes
  • duality
  • computational logic
  • coalgebraic semantics
  • coalgebraic logics
  • categories


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