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Logic Final Review

  1. Nov 19, 2007 #1
    I'm studying for my logic final and I cant seem to find an answer for this practice problem:

    (Using < as proper subset since I dont have the right type)

    T_1 < T_2 < T_3... be a strictly increasing sequence of satisfiable L-Theories.

    a) Show that the union of T_n is satisfiable (over all n in the natural numbers).

    b) Show that the union of T_n is not finitely axiomatizable.

    A) Pretty simple, every finite subset is satisfiable since the largets T_n is satisfiable thus by compactness their entire union is satisfiable.

    B) This is were I have some problems. I'm not sure how to go about showing this. I want to show that any finite amount of sentances can only axiomatize up to T_n and then we can simply show that T_n+1 is not axiomatized. Any ideas on this?

    EDIT: I posted this in the wrong forum apparently, if anyone could move it to the logic section I would appreciate it.
    Last edited: Nov 20, 2007
  2. jcsd
  3. Nov 26, 2007 #2
    The midterm is over though I would still like to know how to solve this problem.
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