Selection Functions, Bar Recursion and Backward Induction

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Bar recursion arises in constructive mathematics, logic, proof theory and higher-type computability theory. We explain bar recursion in terms of sequential games, and show how it can be naturally understood as a generalisation of the principle of backward induction that arises in game theory. In summary, bar recursion calculates optimal plays and optimal strategies, which, for particular games of interest, amount to equilibria. We consider finite games and continuous countably infinite games, and relate the two. The above development is followed by a conceptual explanation of how the finite version of the main form of bar recursion considered here arises from a strong monad of selections functions that can be defined in any cartesian closed category. Finite bar recursion turns out to be a well-known morphism available in any strong monad, specialised to the selection monad.


Original languageEnglish
Pages (from-to)127-168
Number of pages42
JournalMathematical Structures in Computer Science
Issue number2
Early online date25 Mar 2010
Publication statusPublished - 1 Apr 2010


  • Higher-type computability, exhaustible set, Kleene-Kreisel spaces of continuous functionals