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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Preventing type extensions
Date: Thu, 23 Sep 2010 21:00:01 +0100
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> Gosh, it was no more than just this: if horse is an animal that does
> not imply they are interchangeable. Compare: "all horses have hoofs"
> and "all animals have hoofs."

I don't see your point.

You could make a near-infinity of operations on Animal like has-hooves,
has-tentacles etc but that would be silly. The only ops that make sense
at the Animal level are ones shared by all animals.