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<p class="MsoNormal"><b><span style="font-size:12.0pt">Nick writes:<o:p></o:p></span></b></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="quotation"> As software engineers, what conditions would a program have to fulfill to say that a computer was monitoring “itself<o:p></o:p></p>
<p class="quotation" style="margin-left:0in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="quotation" style="margin-left:0in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;font-weight:normal;font-style:normal">It is common for codes that calculate things to periodically test invariants that should hold. For example, a
physics code might test for conservation of mass or energy. A conversion between a data structure with one index scheme to another is often followed by a check to ensure the total number of records did not change, or if it did change that it changed by an
expected amount. It is also possible, but less common, to write a code so that proofs are constructed by virtue of the code being compliable against a set of types. The types describe all of the conditions that must hold regarding the behavior of a function.
In that case it is not necessary to detect if something goes haywire at runtime because it is simply not possible for something to go haywire. (A computer could still miscalculate due to a cosmic ray, or some other physical interruption, but assuming that
did not happen a complete proof-carrying code would not fail within its specifications.)<o:p></o:p></span></p>
<p class="quotation" style="margin-left:0in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;font-weight:normal;font-style:normal">A weaker form of self-monitoring is to periodically check for memory or disk usage, and to raise an alarm if they
are unexpectedly high or low. Such an alarm might trigger cleanups of old results, otherwise kept around for convenience.
<o:p></o:p></span></p>
<p class="quotation" style="margin-left:0in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;font-weight:normal;font-style:normal"><o:p> </o:p></span></p>
<p class="quotation" style="margin-left:0in"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;font-weight:normal;font-style:normal">Marcus<o:p></o:p></span></p>
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