Step by step --- building representations in algebraic logic

    by R. Hirsch and I. Hodkinson

    J. Symbolic Logic 62 (1997) 225-279


    We consider the problem of finding and classifying representations in algebraic logic. This is approached by letting two players build a representation using a game. Homogeneous and universal representations are characterised according to the outcome of certain games. The 'Lyndon conditions' defining representable relation algebras (for the finite case) and a similar schema for cylindric algebras are derived. Finite relation algebras with homogeneous representations are characterised by first order formulas. Equivalence games are defined, and are used to establish whether an algebra is $\omega$-categorical. We have a simple proof that the perfect extension of a representable relation algebra is completely representable. Another two-player game is used to derive equational axiomatisations for the classes of all representable relation algebras and representable cylindric algebras.

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