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The Third Homomorphism Theorem

Jeremy Gibbons

Abstract

The Third Homomorphism Theorem is a folk theorem of the constructive algorithmics community. It states that a function on lists that can be computed both from left to right and from right to left is necessarily a list homomorphism - it can be computed according to any parenthesization of the list. We formalize and prove the theorem, and describe two practical applications: to fast parallel algorithms for language recognition problems and for downwards accumulations on trees.

Details

Journal

Journal of Functional Programming

Note

Earlier version appeared in B. Jay‚C. editor‚ Computing: The Australian Theory Seminar‚ Sydney‚ December 1994‚ 62–6p.9

Number

4

Pages

657–665

Volume

6

Year

1996

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