From: | Michael Glaesemann <grzm(at)seespotcode(dot)net> |
---|---|
To: | Michael Glaesemann <grzm(at)seespotcode(dot)net> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Ranges for well-ordered types |
Date: | 2006-06-10 16:49:49 |
Message-ID: | 963465F7-2C79-4E43-86E6-8AC2EF6E16C6@seespotcode.net |
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Lists: | pgsql-hackers |
On Jun 10, 2006, at 23:51 , Michael Glaesemann wrote:
> A range can be formed for any point type, where a point type is
> any type that's well-ordered:
> * the range of values is bounded (the number of values in the type
> is finite)
> * comparisons are well-defined for any two values, and
> * for any point p, the next point can be found using a successor
> function
It was pointed out to me off list that I got my definition of well-
ordered wrong. I was confusing the definition of well-ordered with
the overall requirements that I was using to define ranges.
Well-ordered is just that for any two values a and b of a given type,
a < b is defined. That's what I was attempting to get at in the
second point above. The added requirements of having the type bounded
(which is going to happen on a computer anyway) and having a
successor function are still required for the range definition, but
not part of the definition of well-orderedness per se.
Michael Glaesemann
grzm seespotcode net
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