Thank you for the above, for my diary! On 24 March 2014 20:14, Bruno Marchal <marc...@ulb.ac.be> wrote: > > New exercise: > > show > > (W,R) respects A -> []<>A > iff > R is symmetrical. >
OK, symmetrical means for all a and b, a R b implies b R a. A -> []<>A can (I hope) be read as "the truth of A in one particular world (which I will call this world) implies that for all worlds accessible from this world, there exists at least one world in which A is true". Well, there is indeed one world accessible from those other worlds, in which A is true - this one! Because all worlds accessible from this one can access this world (due to symmetry) and in this world A is true. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
