On Thu, Jan 16, 2020 at 7:52 AM 'Nil Geisweiller' via opencog <
[email protected]> wrote:
> On 1/16/20 3:22 PM, Alexander Gabriel wrote:
> >
> > So, from looking at the AndLink, I gather that it can only be applied
> > to EvaluationLinks, InheritanceLinks, OrLinks, NotLinks,
> > and ExecutionLinks. Is there a preferred way of how to apply it (and its
> > brethren) to StateLinks, (and PresentLinks, AlwaysLinks and so on)?
>
> I suppose so, just copy/paste it and modify it to your needs.
>
Well, I'd like to disagree slightly with Nil, and urge some caution here.
Not every link type is meant to be (can be, should be) treated as a
function or term in classical predicate logic.
To wax philosophical, just a little bit: the atomspace is meant to be a
kind-of "knowledge representation database" and as such, the goal is to
allow different kinds of systems to be built on it: classical predicate
logic (the "crisp" stuff) but also probabilistic logic ("PLN") but also
things that are not logics at all, and do not have boolean operations like
"and", "or" "not" defined for them (because they aren't evaluatable into
'truth values', or perhaps because they don't have a consistent
interpretation outside of some particular context or frame...)
PresentLinks and AlwaysLinks are "reserved keywords" intended for the
pattern matcher, only. If you defocus your eyes a bit, then sure, they
seem to resemble the predicate-logic "there-exists" and "for-all" . But
the were not designed for reasoning, there were designed for solving the
"subgraph isomorphism problem" and for "term rewriting". So if you actually
need the predicate-logic constructs "there-exists" and "for-all", then you
should use the ThereExistsLink and ForAllLink. (These have been so
under-utilized in the code base that they might have been stripped out; but
they could be added back in. ).
-- Linas
--
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