On Mon, Sep 23, 2013 at 7:49 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:
>
> On 23 Sep 2013, at 12:41, Telmo Menezes wrote:
>
> On Sat, Sep 21, 2013 at 9:43 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:
>
>
> On 21 Sep 2013, at 15:10, Telmo Menezes wrote:
>
>
> 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>
>
>
>
> If so, can't we say ~D~t and thus []t?
>
>
>
> Yes, []t is a theorem, of G and most modal logic, but not of Z!
>
>
>
>
>
> Isn't the only situation where ~Dt the one where this is no world?
>
>
>
> ~Dt, that is [] f, inconsistency, is the type of the error, dream, lie, and
>
> "near-death", or in-a-cul-de-sac.
>
>
> Thus your interest in near-death experiences?
>
>
>
> Yes. And in all "extreme" altered state of consciousness. Those extreme
> cases provide key information.

Can this information be recovered?
For example, is a NDE that did not result in death, was it really a cul-de-sac?

>
>
>
> We should *try* to avoid it, but we can't avoid it without loosing our
>
> universality.
>
>
> The consistent machines face the dilemma between security and lack of
>
> freedom-universality.  With <>p = ~[] ~p, here are equivalent way to write
>
> it:
>
>
> <>t -> ~[]<>t
>
> <>t -> <> [] f
>
> []<>t -> [] f
>
>
> I don't understand how you arrive at this equivalence.
>
>
> I use only the fact that  (p -> q) is equivalent with (~q -> ~p) (the
> contraposition rule, which is valid in classical propositional logic), and
> the definition of <> p = ~[] ~p. I use also that ~~p is equivalent with p.
>
> Note that []p = ~~[]~~p = ~<> ~p.  And,
>
> ~[]p = <> ~p
> and
> ~<>p = [] ~p
>
> Like with the quantifier, a not (~) jumping above a modal sign makes it into
> a diamond, if it was a bo, and a box, if it was a diamond.
>
>
> Starting from <>t -> ~[]<>t.

But where does <>t -> ~[]<>t come from?

> Contraposition gives ~~[]<>t -> ~<>t, and this
> gives by above, []<>t -> []~t, which gives
> []<>t -> []f   (as ~t = f, and ~f = t).
>
> OK?

Ok!

> For the third one, starting from the first one again: <>t -> ~[]<>t, By
> contraposition []<>t -> ~<>t , but ~<>t = []~t = [] f.
>
> OK?

Ok! Thanks Bruno. My only problem now is the above.

Telmo.

> Bruno
>
>
>
> http://iridia.ulb.ac.be/~marchal/
>
>
>
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