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From: Shark8 <OneWingedShark@gmail.com>
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Subject: Re: OT: A bit of Sudoku
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NNTP-Posting-Date: Fri, 13 Jun 2014 15:47:49 UTC
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Date: Fri, 13 Jun 2014 09:47:51 -0600
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Date: 2014-06-13T09:47:51-06:00
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On 13-Jun-14 04:10, Mike H wrote:
> In message <ourmv.598292$hv6.317046@fx17.iad>, Shark8
> <OneWingedShark@gmail.com> writes
>>
>>  -- Definition of "=" returns true when both sides are NULL,
>>  -- returns false when only one side is NULL, and behaves as
>>  -- normal string-equality when neither side is NULL.
> Is this an example where Dmitry's three state logical (True, Uncertain,
> False)  might be useful?
> See <http://www.dmitry-kazakov.de/ada/intervals.htm>
>

No, not really.
You want "=" to behave like "=" on strings, but extended to handle the 
NULL-cases, and that means a standard boolean result.