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 <opencog@googlegroups.com> 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 >> <opencog@googlegroups.com> 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 opencog+unsubscr...@googlegroups.com. >>> To post to this group, send email to opencog@googlegroups.com. >>> Visit this group at 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. >>> For more options, visit 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 opencog+unsubscr...@googlegroups.com. > To post to this group, send email to opencog@googlegroups.com. > Visit this group at 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. > > For more options, visit 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. Ramachandran -- 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 opencog+unsubscr...@googlegroups.com. To post to this group, send email to opencog@googlegroups.com. Visit this group at https://groups.google.com/group/opencog. To view this discussion on the web visit https://groups.google.com/d/msgid/opencog/CACYTDBfsGxXbowYoxEe0zeqcBmabJXUyqG0dTy%2B1-MmO7sGfHA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
