[FOM] more about identities
Harvey Friedman
friedman at math.ohio-state.edu
Wed Feb 7 01:34:18 EST 2007
On 2/6/07 1:06 AM, "George McNulty" <mcnulty at math.sc.edu> wrote:
> The answer is still the same. There is a finite set \Sigma
> of identities in just one operation symbol which is binary
> such that the set of identities which are logical consequences
> of \Sigma form a nonrecursive set. It is also possible to do
> this with two unary operation symbols. On the other hand, it
> cannot be done with just one unary operation symbol (even
> expanded by finitely many constant symbols).
If I recall, didn't MacKenzie find a single equation in a binary operation
symbol whose logical consequences form a nonrecursive set? I don't know the
reference.
Harvey Friedman
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