Proposed Errata 16 (RIF-PRD)

Hi Christian.

I was looking over the proposed errata for RIF ( http://www.w3.org/2005/rules/wiki/Errata 
  ), and I am quite happy with the proposed solution to errata 16.  I  
think, though, that there is a problem.  The proposed operational  
semantics for equality is stricter than the model-theoretic semantics  
of equality.  For example, as I understand it, _a=_b cannot be matched  
under the operational semantics, but it could be true under the model- 
theoretic semantics as long at I(_a)=I(_b), unless of course there is  
a unique name assumption.  I'm not sure of a good way to reconcile the  
two semantics, but perhaps at least a note should be made about the  
inconsistency if the proposed change to the operational semantics is  
made.

Another possible solution would be to allow matching equality formulas  
to sets of facts, but then there is the problem of redefining State of  
the Fact Base to ensure symmetry and transitivity of equality facts.   
It is more complicated, but it is consistent with the model-theoretic  
semantics.

Personally, I like the simplicity of the proposed solution in the  
errata, but I just wanted to point out this potential inconsistency.   
Thanks for addressing previously reported issues in the errata.

Jesse Weaver
Ph.D. Student, Patroon Fellow
Tetherless World Constellation
Rensselaer Polytechnic Institute
http://www.cs.rpi.edu/~weavej3/index.xhtml