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about emp (was: Motion 42: NO)



On 2013-02-06 22:07:15 +0100, Guillaume Melquiond wrote:
> - Finally, the emp decoration seems superfluous to me. There is no point
> in decorating a nonempty interval with an emp decoration (except maybe
> for wreaking havoc in an interval library), so the emp decoration could
> just as well be removed. An empty interval would then be decorated with
> trv when it does not designate a NaI.

IIRC, there can be problems with that. For instance, take zz = g(yy)
where yy is Empty. Since g is defined and continuous on the empty set
yy, one can return zz = (Empty,dac). But now assume that yy wasn't
actually an input, but yy = f(xx) for some non-empty xx, e.g.
sqrt([-2,-1]). So, one would get:

  (g o f)(xx) = (Empty,dac)

which is wrong.

-- 
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)