[FOM] more about identities

[Harvey Friedman]

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