Orchid XP v8 wrote:
> Hmm, OK. That seems simple enough. I guess the problem is that all that 
> relational calculus stuff is abstracted to the point where it's just 
> moving symbols around and it's difficult to determine how this is 
> related to reality.

Um, yes. Indeed, that's precisely exactly why you would use formal 
relational calculus stuff: it's just moving symbols around with no relation 
to reality. That's why you can program computers to do it - that's all 
computers can do.

That's true of most all formal math, tho: everything related to algebra or 
calculus is ultimately moving symbols around with no relation to reality.

>> There are, of course, standard rules of deduction, like
>>   "for all X, pred(X)"
>> is the same as
>>   "not for some X, not pred(X)"
>> and so on.
> 
> But, notably, if X being true implies Y being true, then X being false 
> does not necessarily imply Y being false.

Um, yes? :-) Was that supposed to be a relevant comment?

-- 
   Darren New, San Diego CA, USA (PST)
   My fortune cookie said, "You will soon be
   unable to read this, even at arm's length."

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