# Re: Unexpected Hanging

```On Fri, Sep 20, 2013 at 3:58 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:
>
> On 19 Sep 2013, at 16:51, Telmo Menezes wrote:
>
>> On Thu, Sep 19, 2013 at 4:31 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:
>>>
>>>
>>> On 18 Sep 2013, at 21:45, Telmo Menezes wrote:
>>>
>>>> On Wed, Sep 18, 2013 at 6:13 PM, Bruno Marchal <marc...@ulb.ac.be>
>>>> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 18 Sep 2013, at 11:43, Telmo Menezes wrote:
>>>>>
>>>>>> <snip>
>>>>>>
>>>>>>
>>>>>> But maybe it doesn't. At least some week form of solipsism, where
>>>>>> there is in fact only me, but the notion of "I" is extended. No?
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> I would say that there are as many notion of "I", that there are
>>>>> intensional
>>>>> nuances.
>>>>>
>>>>> The most basic is the 3-I, like when the machine says I have two arms,
>>>>> (Bp),
>>>>> then there is the 1-I, when the machine says that she has two arms, and
>>>>> it
>>>>> is the case that she has two arms (Bp & p), then there is the observer
>>>>> I,
>>>>> when the machine says that she has two arms, and it is possible, not
>>>>> contradictory, for that machine that she has two arms, or equivalently
>>>>> that
>>>>> 0=0 is not a contradiction, Bp & Dp,
>>>>
>>>>
>>>>
>>>>> equivalent with Bp & Dt. Then the
>>>>> "feeler" whioch combines both Dt and "& p".
>>>>
>>>>
>>>>
>>>> Bruno, I don't understand these last two lines. What's Dt? What's a
>>>> feeler?
>>>
>>>
>>>
>>> A feeler is someone who feels. My automated spelling verifier does not
>>> complain, but perhaps he get tired with me :)
>>
>>
>> Ok. No, it's right. I just thought there was something more to it.
>
>
> Nice!
>
>
>
>
>>
>>> D is for diamond. Dp, in modal logic, often written <>p is an
>>> abbreviation
>>> of ~B~p.
>>
>>
>> I know, I meant Dt vs. Dp. Was it a typo? Otherwise what's Dt as opposed
>> to Dp?
>
>
> OK, sorry. "t" is for the logical constant true. In arithmetic you can
> interpret it by "1=1". I use for  the logical constant false.
>
> As the modal logic G has a Kripke semantics (it is a so-called normal modal
> logic), The intensional nuance Bp & Dp is equivalent with Bp & Dt. "Dt" will
> just means that there is an accessible world, and by Bp, p will be true in
> that world.```
```
Ok, thanks.
If there is one or more accessible worlds, why not say []t? (I'm using
[] for the necessity operator)
Is there any conceivable world where D~t? If so, can't we say ~D~t and thus []t?
Isn't the only situation where ~Dt the one where this is no world?

>
>
>
>>
>>> For example (possible p) is the same as (not necessarily not p). Like "it
>>> exists x such that p(x)" is the same as not for all x do e have not p(x).
>>>
>>> Bp & Dp, really means that p is true in all worlds (that I can access)
>>> and
>>> Dp really means that there is such a world (if not, classically Bp can be
>>> vacuously true). Normally there will be some explanations of modal logic
>>> (on
>>> FOAR). Older explanations on this list exists also, may be by searching
>>> on
>>> "modal" (hmm... you will probably get too many posts ...).
>>
>>
>> I've been slowly going through Chellas.
>
>
> It is a very good book. Boolos 1979 (and 1993) sum up very well Modal Logic
> too.
>
>>
>> Thanks!
>
>
> Welcome!
>
>
> Bruno
>
>
>
> http://iridia.ulb.ac.be/~marchal/
>
>
>
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