On 07 Jun 2012, at 01:58, Russell Standish wrote:


I've deleted the previous thread,


It is possible to delete thread? Including my posts? That should not be possible.

so I've started a new one on modal
logic's "metaaxiom".


IIUC, if I have p (true in a world), and by dint of whatever
convoluted steps, I have


then it is also true that []q (q must be true in all worlds)?

Not necessarily. It can depend on what axioms are used on "p/q". Nor is it necessary that you get p -> q, nor p-> []q. Modal logic does not obey to the deduction theorem.

In fact we have p/p for any p. If you were correct we would have []p for any p.

Could this also be written

---  ?

I don't see any reason for this.



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