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From: Christoph Grein <christoph.grein@eurocopter.com>
Newsgroups: comp.lang.ada
Subject: Re: ToString?
Date: Thu, 14 Mar 2002 07:05:05 +0100 (MET)
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Date: 2002-03-14T07:05:05+01:00

From: Jeffrey Carter <jeffrey.carter@boeing.com>

> > Ah, the '0' isn't a positive number thang!
>
> It's easy enough to test:
> 
> with Ada.Text_IO;
> use Ada.Text_IO
> procedure Is_Zero_Positive is
>    Zero : constant := 0;
> begin -- Is_Zero_Positive
>    if Zero in Positive then
>       Put_Line ("Zero is Positive");
>    else
>       Put_Line ("Zero is not Positive");
>    end if;
> end Is_Zero_Positive;
> 
> This puts "Zero is not Positive" to the standard output. QED.

You mean a test or a mathematical proof? For a test, this is OK.

For a proof, you have to prove first that Positive holds only
positive numbers :-)

Perhaps you also have to prove that the symbol 0 you use up there is really a 
representation of what you have in mind when speaking about the mathematical 
object called 0 :-)