Re: Documentation for SORT

[Ben Pfaff]

John Darrington <address@hidden> writes:

> The documentation for sort says.
>
>  The sort algorithms used by @cmd{SORT CASES} are stable.  That is,
>  records that have equal values of the sort variables will have the
>  same relative order before and after sorting.  As a special case,
>  re-sorting an already sorted file will not affect the ordering of
>  cases.
>
> The last sentence confuses me.   Why is it a special case?  Isn't that
> property necessary for a stable sort?

The property that re-sorting an already sorted file will not
affect the ordering of cases is a special case of the properties
of a stable sort.  See http://en.wikipedia.org/wiki/Special_case

(It's not an exceptional case, just a particular instance of the
rule.)
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