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Equivalences and Congruences on Infinite Conway Games∗

Published online by Cambridge University Press:  02 March 2012

Furio Honsell ,
Marina Lenisa  and
Rekha Redamalla
Furio Honsell
Affiliation:
Dipartimento di Matematica e Informatica, Università di Udine, Viale delle Scienze 206, 33100 Udine, Italy. furio.honsell@comune.udine.it; marina.lenisa@uniud.it
Marina Lenisa
Affiliation:
Dipartimento di Matematica e Informatica, Università di Udine, Viale delle Scienze 206, 33100 Udine, Italy. furio.honsell@comune.udine.it; marina.lenisa@uniud.it
Rekha Redamalla
Affiliation:
Birla Science Centre, Adarsh Nagar, 500063 Hyderabad, India; rrekhareddy@yahoo.com
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Abstract

Taking the view that infinite plays are draws, we study Conwaynon-terminating games and non-losing strategies. These admit asharp coalgebraic presentation, where non-terminating games are seen as afinal coalgebra and game contructors, such as disjunctivesum, as final morphisms. We have shown, in a previous paper,that Conway’s theory of terminating games can be rephrased naturally in terms of game(pre)congruences. Namely, various conceptually independent notions ofequivalence can be defined and shown to coincide on Conway’sterminating games. These are the equivalence induced by the ordering on surrealnumbers, the contextual equivalence determined by observingwhat player has a winning strategy, Joyal’s categoricalequivalence, and, for impartial games, the denotationalequivalence induced by Grundy semantics. In this paper, wediscuss generalizations of such equivalences to non-terminating games andnon-losing strategies. The scenario is even more rich and intriguing inthis case. In particular, we investigate efficient characterizations of the contextualequivalence, and we introduce a category of fair strategies and acategory of fair pairs of strategies, both generalizing Joyal’s categoryof Conway games and winning strategies. Interestingly, the category of fair pairs capturesthe equivalence defined by Berlekamp, Conway, Guy on loopy games.

Keywords

Conway gamesnon-wellfounded gamescoalgebrasequivalencesJoyal’s category
Type
Research Article
Information
RAIRO - Theoretical Informatics and Applications , Volume 46 , Issue 2: 12th Italian Conference on Theoretical Computer Science(ICTCS) , April 2012 , pp. 231 - 259
Copyright
© EDP Sciences 2012

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