🚀 go-pugleaf

In article <1aaaouINN9vp@usenet.INS.CWRU.Edu> cxm7@po.CWRU.Edu (Colin Mclarty) writes:
>
>In a previous article, chinnici@ghost.dsi.unimi.it (roberto riccard chinnici) says:
>> (read earlier article for problem.)
>	to find gn for n in J, start evaluating psi for each m in I.
>Of course you can not just start with the first m in I and evaluate 
>psi for it, since psi might be undefined for it.  So take a few steps 
>on the first element of I, then a few on the second, then a few more 
>on the first, a few more on the second and a few on the third, then a
>few more on the first....  This way we would eventually find the value 
>of psi for each element of I where it is defined.  Since psi maps I 
>onto J we will eventually finish evaluating psi on some element of I 
>that gives n.  Define gn to be that element.  

This argument requires that I be r.e.  Otherwise, one could not
carry out the first step: ``start evaluating psi for each m in I''.
A little thought indicates that failing to exclude N-I from the
computation can lead to failure.  In fact, it is easy to construct
co-r.e. I satisfying chinnici's conjecture; see my earlier post.

Mark
-- 
Mark A. Fulk			University of Rochester
Computer Science Department	fulk@cs.rochester.edu