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Operations and equations for coalgebras

Published online by Cambridge University Press:  28 January 2005

ALEXANDER KURZ
Affiliation:
Department of Computer Science, University of Leicester, UK
JIŘÍ ROSICKÝ
Affiliation:
Masaryk University, Janáčkovo nám. 2a, 662 95 Brno, Czech Republic

Abstract

We show how coalgebras can be presented by operations and equations. This is a special case of Linton's approach to algebras over a general base category ${\cal X}$, namely where ${\cal X}$ is taken as the dual of sets. Since the resulting equations generalise coalgebraic coequations to situations without cofree coalgebras, we call them coequations. We prove a general co-Birkhoff theorem describing covarieties of coalgebras by means of coequations. We argue that the resulting coequational logic generalises modal logic. This relies on the fact that coalgebraic operations respect an appropriate notion of bisimulation and can be considered as modal operators.

Type
Paper
Copyright
2005 Cambridge University Press

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