Subject: Re: [xsl] () eq () vs () = () From: Michael Kay <mike@xxxxxxxxxxxx> Date: Mon, 03 Oct 2011 14:35:27 +0100 |
Um no. Another surprise is that (every $x in X satisfies P) doesn't imply (some $x in X satisfies P). If X is empty, then the first proposition is inevitably true, while the second is inevitably false. Logic is full of pitfalls.Heh, nice. So:It's a common misunderstanding about universal quantification. The proposition
every S satisfies P
is always true when S is empty, regardless of P.
For example, the statement "every hotel on St Kilda is fully booked" is true, as is the statement "every hotel on St Kilda has vacancies" (there are no hotels on St Kilda).
every hotel on St Kilda is fully booked, yet some hotel on St Kila isn't fully booked.
Michael Kay Saxonica
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