[FOM] Questions on axiomatizations of complete theories
joeshipman@aol.com
joeshipman at aol.com
Sat Mar 4 22:16:01 EST 2006
In the following, T always refers to a complete theory which is
recursively axiomatizable (hence decidable) but not finitely
axiomatizable.
Say that an axiomatization A = {A1, A2, ...} of T is "tight" if every
axiom in it is logically independent of the rest.
Say that A = {A1, A2, ...} is "loose" if any infinite subset of A
implies all the axioms in A.
These are two extremes. Every axiomatizable theory has a "loose"
axiomatization: convert {A1, A2, A3, ... } to {A1, A1&A2, A1&A2&A3,
...}.
Can anyone find nontrivial examples of T (preferably theories that are
already considered interesting) such that
1) No recursive axiomatization of T is tight?
2) Every recursive axiomatization of T contains a recursive "loose"
subset?
-- JS
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