Is %i an integer? - Adding more facts to the database


On Mon, 29 Jun 2009, Robert Dodier wrote:

< On 6/28/09, Stavros Macrakis <macrakis at alum.mit.edu> wrote:
< 
< > On Sun, Jun 28, 2009 at 5:53 PM, Leo Butler <l.butler at ed.ac.uk> wrote:
< >
< >> ...It seems to me that there is a convention and it is reasonable:
< >> if x is declared to be in a set, but not explicitly declared to be
< >> in a subset, then it is assumed not to be in the subset.

Let me clarify that I ought to have said `for purposes of inference, if
x is declared to be in a set, but not explicitly declared to be in a
subset, then it is not assumed to be in the subset or its complement.
And maxima transposes `not assumed` to `assumed not`.'

declare(n,real);
featurep(n,real);
true
featurep(n,irrational);
false
featurep(n,rational);
false

So 'false' actually means both false or unknown, depending on the
context.
< >
< > I think that would be a *terrible* convention and it conflicts with standard
< > mathematics: writing x ?? *C** never* implies x ?? *R *in mathematics.

I can't read the second part of what you wrote. However, you can
see that it is the convention maxima utilises.

< 
< I agree that's terrible as stated, but it makes more sense
< if the test function (at present featurep(x, foo)) means only
< "I can demonstrate x has feature foo".
< Returning false means only that the demonstration fails,
< not that the negation can be demonstrated.

Yes, this is what I had in mind.

Leo
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