[std-interval] More on interval computations as proofs

Dr John Pryce j.d.pryce at ntlworld.com
Wed Oct 4 20:26:24 PDT 2006

Dear all

At 00:58 30/09/06, Ron Avitzur wrote:
>>The discussion showed that Standard functions MUST set a flag when
>>the argument interval is not completely contained in the domain of
>>the function. Otherwise (i.e without the flag) verification of the
>>result with fixed points or other assertions that need continuity is
>>not possible
>For my graphics application of intervals, as well, it is also
>sometimes necessary to track both continuity of functions and
>the domain over which they are well-defined.

At first I thought it useful to have two separate flags, one for 
defined and one for continuous, but in all the applications I have 
considered, it sufficed to check for the function being (defined AND 
continuous) on its input box. I.e. only have one flag.

Does anyone have an example to the contrary?


Dr John and Mrs Kate Pryce
142 Kingshill Rd
Swindon, Wiltshire SN1 4LW
Tel (+44)1793-331062

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