is one of the books that it is talking about. this is something new, and something that we have not seen before -- we can have multiple reference tables that talk about other reference tables.
what this means in practice is that we can have strings of boxes and/or diamonds. for instance, we can have ◇◇x. the diamonds don't work any differently. what ◇◇x tells us is that there's a table on which we can find ◇x; and then ◇x on that table tells us that there's a table on which we can find x.
this can be tricky. in our example, every book is talking about every book, but this might 