Composition Theorem for Generalized Sum

  • Authors:
  • Alexander Rabinovich

  • Affiliations:
  • School of of Computer Science, Sackler Faculty of Exact Sciences, Tel Aviv University, Israel. E-mail: rabinoa@post.tau.ac.il

  • Venue:
  • Fundamenta Informaticae
  • Year:
  • 2007

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Abstract

Composition theorems are tools which reduce sentences about some compound structure to sentences about its parts. A seminal example of such a theorem is the Feferman-Vaught Theorem [3] which reduces the first-order theory of generalized products to the first order theory of its factors and the monadic second-order theory of index structure. Shelah [23] used the composition theorem for linear orders as one of the main tools for obtaining very strong decidability results for the monadic second-order theory of linear orders. The main technical contribution of our paper is (1) a definition of a generalized sum of structures and (2) a composition theorem for first-order logic over the generalized sum. One of our objectives is to emphasize the work-out of the composition method.