I think we are mis-communicating about something. Whatever it is that the URE is doing, it isn't alpha-conversion, its something else. There's no code outside of the atomspace that is algorithmically capable of performing alpha-conversion. It's literally impossible to accomplish, it simply has no access to those atoms.
--linas On Thu, Nov 17, 2016 at 1:51 AM, 'Nil Geisweiller' via opencog < [email protected]> wrote: > > > 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. >> Don’t >> polish the brass on the bandwagon.” – V. S. 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