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Re: [ontolog-forum] 3D+1 (was presentism...was blah blah blah)

To: ontolog-forum@xxxxxxxxxxxxxxxx
From: Wacek Kusnierczyk <waku@xxxxxxxxxxx>
Date: Fri, 04 Feb 2011 10:50:19 -0600
Message-id: <4D4C2E4B.8050602@xxxxxxxxxxx>
On 2/4/11 10:15 AM, Yu Lin wrote:
> Hi, Waclaw,
> I think I might be wrong in using the symbol here.
> If you state that C(c,t) = C@t(c) and it means: c at time t is
> instance of C. I think there is no big difference between what in our
> mind.    (01)

The problem I have with your 'means' part is that it is not clear to me 
which of Pat's three versions it really is. (Presumably not the 
sentence-true-at-t one, the 3D one.)    (02)

> When you say :">      c1 (is instance at t) of C",
> it seems that you denied that c1 as an instance has no timestamp.    (03)

I just don't know what this timestamp is, so it's hard to deny it.    (04)

> Can I infer from  "c1 (is instance at t) of C" to say that, c1 (is
> instance at t2) of C2?    (05)

With no extra information, I can't see how this would follow.    (06)

> Back to Pat's statement:
> 2. Attach it to the relation as an extra argument, and call the
> relation a 'fluent': R(a, b, t) This gives you the classical AI/KR
> approach which used to be called the situation calculus, where one
> quantifies over times in the KR language itself, but the object terms
> are still thought of as denoting 3D rather than 4D entities. Call this
> 3D+1.
> --- what the t denotes is not clear here.    (07)

I can't speak for Pat, but it seems to me he meant time.    (08)

> And you given R@t(a,b), which is clearer than above,    (09)

It's just a fancifully proposed syntactic variant.  (Perhaps this sort 
of syntax is actually in use, but not to my, rather limited, 
knowledge).  What is clearer here?    (010)

> dose it mean that:
> 1. at time t1, there is a R between a and b is true.    (011)

R@t(a,b) is supposed to mean that at t the relation R holds between a 
and b.  This is what I think is a sensible reading of R(a, b, t).  
(Though the latter is likely more literally read as 'R holds for a, b, 
and t').    (012)

As for the 'is true' part, you should perhaps be more careful.  Using 
IKL (google for IKL if you're not familiar), these two    (013)

     (R a b t)
     ((that (R a b t)))    (014)

are equivalent, though literally the former says 'R holds for a, b, and 
t', while the latter says 'the proposition that R holds for a, b, and t 
is true'.    (015)

> 2. at time t2, there is a R' between a and b is also true.?    (016)

And how does R@t(a,b) relate to t2 and R'?    (017)

vQ    (018)

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