Re: Clean Object Class Design -- Circle/Ellipse

In article <bdf69bdf.0107251244.2c056242_at_posting.google.com>, Mikito Harakiri says...
>
>marc.gluch_at_mindtap.com (Marc Gluch) wrote in message news:<3b5ad464.1618119793_at_news.grpvine1.tx.home.com>...
>>
>> Since operations on circles and elipses are hard to agree on
>> (in absence of a context of a specific application area and a formal
>> specification of these ops), I suggested considering an equivalent
>> question of:
>> Is IA=<I,{+,*}> a subtype of RA=<R,{+,*}> in the "real" world (math)?
>> The "real" world answer is no, but Date's reasoning (?) would lead
>> to qualified yes (integers are reals, but the set of update operations
>> that apply to integer variables is neither a subset nor a superset of
>> the set of such operations that apply to real variables).
>
>Somebody in the other thread noted that subsets in math are defined by
>predicates over containing set. I have trouble identifying a predicate
>that selects integers from the set of real numbers. Am I missing
>something obvious?

Yes you do: density. Here is the predicate

exists x and y and not exists z such that x < z < y

"Less than" is also a part of number signature. Received on Wed Jul 25 2001 - 22:57:00 CEST