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authorNorbert Preining <norbert@preining.info>2019-09-02 13:46:59 +0900
committerNorbert Preining <norbert@preining.info>2019-09-02 13:46:59 +0900
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+Date: 07 Jul 1993 12:45:34 -0400 (EDT)
+From: Michael Downes <MJD@MATH.AMS.ORG>
+Subject: Around the Bend #9, answer
+Sender: ITeX-Mgr@SHSU.edu
+To: info-tex@shsu.edu
+Reply-to: Michael Downes <MJD@MATH.AMS.ORG>
+Message-id: <742063535.36965.MJD@math.ams.org>
+X-ListName: TeX-Related Network Discussion List <INFO-TeX@SHSU.edu>
+
+"In internal vertical mode, if the preceding item on the list is a
+"vbox, can you do this: \unvbox\lastbox?
+
+The answer is no. If you tried it, you would have seen the error
+message:
+
+ ! Missing number, treated as zero.
+ <to be read again>
+ \lastbox
+ l.3 \unvbox\lastbox
+
+ ? h
+ A number should have been here; I inserted `0'.
+ (If you can't figure out why I needed to see a number,
+ look up `weird error' in the index to The TeXbook.)
+
+\lastbox does not return a box register number, which is what \unvbox
+requires; instead, \lastbox returns a <box> object in the sense of the
+TeXbook, chapter 24, p 278. There are only a few TeX commands that
+accept a <box> object as their argument (\shipout, \setbox, \leaders,
+...), and \unvbox is not one of them.