John Cowan wrote:

> Sudarshan S Chawathe scripsit:
>
> >   (make-comparator exact-integer?
> >   		   =
> > 		   (lambda (i j)
> >                      (and (even? i)
> >                           (even? j)
> >                           (< i j)))
> > 		   number-hash)
>
> This clearly violates the programmer's responsibilities section, as
> I said before.  The ordering predicate is required to be asymmetric.
> An asymmetric predicate is one in which, for all values of a and b,
> if (pred a b) is true than (pred b a) is false.  This is obviously not
> true here, so what you have is a comparator whose behavior when passed
> to standard routines is undefined.

I agree that the SRFI requires the ordering predicate to be
asymmetric.  I also agree with your definition of asymmetric
predicates.

However, I do not understand why you claim that the ordering predicate
in the above example (let's call it 'e<') is not asymmetric.  Using
your definition, could you please exhibit values of 'a' and 'b' for
which (e< a b) is true and (e< a b) is not false?  (If your claim is
true then at least one such pair a,b must exist.)

I have similar comments about the other example in my earlier message,
but perhaps it's best to focus on this one here.

Regards,

-chaw