On 11/17/2016 09:09 AM, Ben Goertzel wrote:
I think our conclusion in 2015 was that processes like the chainer should do alpha conversion on the fly... so we should supply a utility function making it easy for anyone to invoke alpha conversion in a particular set of atoms..
The URE does alpha-conversion whenever necessary as to avoid name capture, there's no problem here. The problem comes from the fact that the atomspace may silently perform alpha-conversion when a scope link is added, ultimately there are solutions to address any problem resulting from such implicit conversions, but I can't help it, there's a part of me that feels ambivalent about it...
Anyway, I'll open a github issue whenever I encounter the problem I'm trying to describe in real life situation.
Nil
On Nov 17, 2016 3:54 PM, "'Nil Geisweiller' via opencog" <[email protected] <mailto:[email protected]>> wrote: The reason I didn't want to open a bug report just yet is because I wanted to discuss whether we really want to check alpha-equivalence whenever a new scope link is added to the atomspace (and subsequently consider both equal and return the previous one to the user). Nil On 11/17/2016 05:13 AM, Linas Vepstas wrote: Look, if there is a bug, open a bug report. I'm nervous about these kind of blanket statements about what's best and what is not best. The atomspace is already complicated, adding more complexity to it is not a solution. --linas On Wed, Nov 16, 2016 at 8:27 PM, Ben Goertzel <[email protected] <mailto:[email protected]> <mailto:[email protected] <mailto:[email protected]>>> wrote: Nil, I just reviewed our dialogue on this from a year ago... It seems what we provisionally concluded there was that the chainer should do alpha-conversion on the fly in the course of pattern matching ... but that the Atomspace shouldn't do alpha-conversion "automatically" in any other sense [unless we want to add some Reduct type engine on the Atomspace, which could do alpha-conversion along with other normalizations, but that becomes a separate issue] We also discussed a cog-new-var command that could be used to minimize the complexities of alpha-conversions... (via reducing the incidence of redundant variable names) In this case, the alpha-conversion done by the chainer in the course of doing its business, would need to handle LocalQuoteLink correctly... The choice of the chainer to do alpha-conversion but not (yet) more general types of reduction, would be made because alpha-conversion is cheaper and easier and of such broad utility. Later versions of the chainer might do more general reductions as part of their ordinary business, as well... I may be missing something; a year ago when William and I were talking about this, my head was fully immersed in the problem, but it's less the case right now... -- Ben On Wed, Nov 16, 2016 at 8:34 PM, 'Nil Geisweiller' via opencog <[email protected] <mailto:[email protected]> <mailto:[email protected] <mailto:[email protected]>>> wrote: > I'm back to this issue. > > The notion of LocalQuote is indeed incompatible with systematic > alpha-conversion. > > Consider this pattern > > (Get > (VariableList > (TypedVariable > (Variable "$X") > (Type "TypedVariableLink")) > (TypedVariable > (Variable "$P") > (Type "PredicateNode")) > (TypedVariable > (Variable "$Q") > (Type "PredicateNode")) > (LocalQuote > (ImplicationScope > (Variable "$X") > (Variable "$P") > (Variable "$Q")))) > > This fetches ImplicationScope links. > > If the following > > (ImplicationScope > (Variable "$X") > (Variable "$P") > (Variable "$Q")) > > happen to be alpha-equivalent to something with different variable names it > will render the Bind link invalid. > > Indeed alpha-conversion shouldn't be triggered in that case, the right idea > is that the ImplicationScope, when quoted corresponds to a DIFFERENT atom > than the one not being quoted. Also of course if we decide to not perform > systematic alpha-conversion then this problem doesn't arise. > > I'm re-iterating my question. Do we really want automatic alpha-conversion > to begin with? > > If the answer is yes then I suppose we need a way to tell that the quoted > version is different than then unquoted version. > > Nil > > > On 10/22/2016 03:34 AM, Ben Goertzel wrote: >> >> Nil, >> >> Just brainstorming here, but perhaps the command for adding an Atom >> should have an option that the user can set, which determines whether >> the results would be alpha-converted or not >> >> The default would be to do the alpha-conversion (which would be >> appropriate if the variable names are say randomly generated, and thus >> of no particular importance to the user -- the alpha conversion is >> then just preventing odd collisions between randomly generated >> variable names created by two different processes) >> >> However, if the user wants they can override this default and specify >> "no alpha conversion", and then it is their responsibility to check >> and be sure their chosen VariableNode names are not going to be used >> in a way that creates some conflict ... >> >> This option would need to be added to Scheme, python, Haskell >> bindings, but also to the core API for adding scoped links, I guess... >> >> I am only about 83.456% sure I understand the problem here... >> >> -- Ben >> >> >> >> On Fri, Oct 21, 2016 at 11:55 PM, 'Nil Geisweiller' via opencog >> <[email protected] <mailto:[email protected]> <mailto:[email protected] <mailto:[email protected]>>> wrote: >>> >>> Hi, >>> >>> I start to think that automatic alpha-conversion is evil. >>> >>> First let me recall what it does. Say you've added >>> >>> (Scope (VariableList (Variable "$X") (Variable "$Y")) >>> (And (Variable "$X") (Variable "$Y"))) >>> >>> and you subsequently add >>> >>> (Scope (And (Variable "$gold") (Variable "$silver"))) >>> >>> then recalling the handle of that last addition, you'd get the first >>> alpha-equivalent scope, which is >>> >>> (Scope (VariableList (Variable "$X") (Variable "$Y")) >>> (And (Variable "$X") (Variable "$Y"))) >>> >>> This is rather confusing to the user, but even worse the pattern matcher >>> behaves differently with the former or the latter. If you use the former >>> to >>> match grounds containing variables "$X" and "$Y" it may not work due to >>> the >>> pattern matcher discarding self-matches. The latter would match UNLESS >>> the >>> former has been previously added, because the variables "$gold" and >>> "$silver" would be silently replaced by "$X" and "$Y". This is horribly >>> confusing to the user! >>> >>> Second, it seems rather arbitrary to try to detect this kind of >>> equivalence >>> while there's an infinity of others. For instance >>> >>> (And (Variable "$X") (And (Variable "$Y")) >>> >>> is equivalent to >>> >>> (And (Variable "$X") (Variable "$Y")) >>> >>> For these reasons I think semantic equivalence detection shouldn't be >>> incorporated into the AtomSpace. The AtomSpace should take care of the >>> syntax only (OK, with the exception of unordered links), as it's always >>> been, and this task should differed to another process working above the >>> AtomSpace. >>> >>> It was suggested a while ago to have a normal form reduction engine for >>> the >>> AtomSpace, similar to MOSES', and such an engine could be used to reduce >>> while adding atoms, if the user chooses so. This is a much cleaner way to >>> handle that. Also since semantic equivalence is undecidable, there will >>> always be a battle between completeness and performance. Another reason >>> to >>> have this ever growing monster above the AtomSpace rather than in it. >>> >>> OK, I don't know if I've convinced you, or even if I've convinced myself, >>> but it's really a discussion we need to have. >>> >>> Opinions welcome. >>> >>> Nil >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "opencog" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to [email protected] <mailto:opencog%[email protected]> <mailto:opencog%[email protected] <mailto:opencog%[email protected]>>. >>> To post to this group, send email to [email protected] <mailto:[email protected]> <mailto:[email protected] <mailto:[email protected]>>. >>> Visit this group at https://groups.google.com/group/opencog <https://groups.google.com/group/opencog> <https://groups.google.com/group/opencog <https://groups.google.com/group/opencog>>. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/opencog/580A3A75.1020708%40gmail.com <https://groups.google.com/d/msgid/opencog/580A3A75.1020708%40gmail.com> <https://groups.google.com/d/msgid/opencog/580A3A75.1020708%40gmail.com <https://groups.google.com/d/msgid/opencog/580A3A75.1020708%40gmail.com>>. >>> For more options, visit https://groups.google.com/d/optout <https://groups.google.com/d/optout> <https://groups.google.com/d/optout <https://groups.google.com/d/optout>>. >> >> >> >> > > -- > You received this message because you are subscribed to the Google Groups > "opencog" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] <mailto:opencog%[email protected]> <mailto:opencog%[email protected] <mailto:opencog%[email protected]>>. > To post to this group, send email to [email protected] <mailto:[email protected]> <mailto:[email protected] <mailto:[email protected]>>. > Visit this group at https://groups.google.com/group/opencog <https://groups.google.com/group/opencog> <https://groups.google.com/group/opencog <https://groups.google.com/group/opencog>>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/opencog/582C444E.4030706%40gmail.com <https://groups.google.com/d/msgid/opencog/582C444E.4030706%40gmail.com> <https://groups.google.com/d/msgid/opencog/582C444E.4030706%40gmail.com <https://groups.google.com/d/msgid/opencog/582C444E.4030706%40gmail.com>>. > > For more options, visit https://groups.google.com/d/optout <https://groups.google.com/d/optout> <https://groups.google.com/d/optout <https://groups.google.com/d/optout>>. -- Ben Goertzel, PhD http://goertzel.org “I tell my students, when you go to these meetings, see what direction everyone is headed, so you can go in the opposite direction. 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