Re: [test] disjunctive entailment without equality

On Sat, 29 Nov 2008 22:39:24 -0500
Chris Welty <cawelty@gmail.com> wrote:

> 
> 
> Thanks, Jos.
> 
> This gets me wondering.  Clearly the converse of Jos' test case also holds,
> e.g. that:
> 
> Document(
>   Prefix(ex http://example.com/example#)
>   Prefix(pred http://www.w3.org/2007/rif-builtin-predicate#)
>   Group(
>     ex:p(ex:a)
>     Forall ?x (q(?x) :- And (ex:p(?x) External(pred:isInteger(ex:a))))))
> 
> |= (or q(ex:a) External(pred:isNotInteger(ex:a)))

Why is this outside the language?

The problem here is that without
any kind of closed-world assumption or a unique name assumption the above leads
to a disjunction, which cannot be taken apart, unlike in logic programming.

So, with negative guards we are introducing negation through the back door, but
do not inject the standard antidotes to keep disjunction away.

michael