Re: Clean Object Class Design -- Circle/Ellipse

In article <woG77.6847$ar1.22998_at_www.newsranger.com>, Vadim Tropashko says...
>
>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.

This is not what I meant. You gave me an axiom which is true for integers but false for reals. Could you please write a predicate with one free variable that defines a subset of integers given a set of real numbers? Received on Wed Jul 25 2001 - 23:13:29 CEST