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Re: H-closed axiomatizable classes

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  • henkcsaba
    Thank you, Keith & Steve, Csaba
    Message 1 of 5 , Mar 5, 2002
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      Thank you, Keith & Steve,

      Csaba

      --- In univalg@y..., "k_kearnes" <kearnes@e...> wrote:
      > Csaba, John-
      >
      > The empty class of structures is closed under homomorphic
      > images but is not axiomatizable by positive sentences.
      > But if K is a nonempty axiomatizable class, then it is
      > closed under homomorphic images iff it is positively
      > axiomatizable. (Thm 3.2.4 of Chang & Keisler.)
      >
      > Yours,
      > Keith
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