Re: OWL 2 RL in RIF (Second Edition) 4.3.2 Property chain rule

I've recorded this as Proposed Erratum 1 on 
https://www.w3.org/2001/sw/wiki/RIF_Errata.   Feel free to expand on it 
there.

One could read several different things into the first erratum in the 
Second Edition coming 4.5 years after publication.

       -- Sandro

On 08/31/2017 05:10 PM, Dave Reynolds wrote:
> On 30/08/17 23:44, Reinhard Schrage wrote:
>>
>> Hello,
>>
>> Below RIF Core rule set reads:
>>
>> *4.3.2 Property chain rule *
>>
>> (* <#prp-spo2> *)
>>
>> Forall ?p ?last ?pc ?start (
>>
>>  ?start[?p->?last] :- And (
>>
>>  ?p[owl:propertyChainAxiom->?pc]
>>
>> _checkChain(?start ?pc ?last) ))
>>
>> Forall ?start ?pc ?last ?p ?tl (
>>
>> _checkChain(?start ?pc  ?last) :- And (
>>
>>      ?pc[rdf:first->?p rdf:rest->?tl]
>>
>>  ?start[?p->?next]
>>
>> _checkChain(?next ?tl ?last) ))
>>
>> Forall ?start ?pc ?last ?p (
>>
>> _checkChain(?start ?pc  ?last) :- And (
>>
>>  ?pc[rdf:first->?p rdf:rest->rdf:nil]
>>
>>  ?start[?p->?last] ))
>>
>> Variable ?next is free in second universal rule, yet does not appear 
>> in Forall quantification part.
>>
>> Am I missing something here, or shouldn’t it read e.g.:
>>
>>   Forall ?next ?start ?pc ?last ?p ?tl (
>>
>> _checkChain(?start ?pc  ?last) :- And (
>>
>>      ?pc[rdf:first->?p rdf:rest->?tl]
>>
>>  ?start[?p->?next]
>>
>> _checkChain(?next ?tl ?last) ))
>>
>
> Agreed, looks like a bug.
>
> Dave
>