If the Atomspace does silently perform alpha-conversion upon Atom
insertion, I don't see why any technical problem would occur as a
result of this?
If a human inserts some VariableNodes with names that she likes, it's
obnoxious for the Atomspace to automagically rename these ... for this
reason it seems that automatic alpha-conversion on insertion is
somewhat problematic .... Though I guess one could create a
workaround like
NamedVariableNode "F"
which allows creation of VariableNodes whose names won't be changed..
or we could just accept that VariableNodes may get renamed by the
system and do stuff like
ReferenceLink
LabelNode "F"
VariableNode "12345"
where the "12345" name can be revised by the system if it wants to...
ben
On Thu, Nov 17, 2016 at 4:51 PM, 'Nil Geisweiller' via opencog
<opencog@googlegroups.com> 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"
>> <opencog@googlegroups.com <mailto:opencog@googlegroups.com>> 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 <b...@goertzel.org
>> <mailto:b...@goertzel.org>
>> <mailto:b...@goertzel.org <mailto:b...@goertzel.org>>> 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
>> <opencog@googlegroups.com <mailto:opencog@googlegroups.com>
>> <mailto:opencog@googlegroups.com
>>
>> <mailto: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
>> <mailto:opencog@googlegroups.com>
>> <mailto:opencog@googlegroups.com
>>
>> <mailto: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
>> >>>
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>> Ben Goertzel, PhD
>> http://goertzel.org
>>
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