On 07 Jun 2012, at 01:58, Russell Standish wrote:
Bruno,
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".
OK.
IIUC, if I have p (true in a world), and by dint of whatever
convoluted steps, I have
p
--,
q
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
<>p
--- ?
[]q
I don't see any reason for this.
Bruno
http://iridia.ulb.ac.be/~marchal/
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