[texhax] help with identifying some macros

[Reinhard Kotucha]

On 15 October 2009 P. R. Stanley wrote:

 > Hi folks
 > \strut, \vtop and lblot. I'd be grateful for a brief description of 
 > each, more precisely, the general effect on the presentation.
 > 
 > Here's an example of two of them in use taken from The Z Notation: a 
 > Reference Manual by Michael Spivey.
 > 
 > $birthday$:
 > \[
 > 	known = \{\,{\rm John, Mike, Susan}\,\} \\
 > \also
 > 	birthday = \{\,\vtop{\halign{\strut#\hfil&${}\mapsto{}$#\hfil\cr
 > 			John&  25--Mar,\cr
 > 			Mike&  20--Dec,\cr
 > 			Susan& 20--Dec\,\}.\cr}}
 > \]
 > Truth be told I've seldom come across anything so cryptic. For 
 > example, what does the "#" signify?

I can't answer your questions better than Barbara.  

If you need more information about plain TeX. it's advisable to
consult a tutorial.  A few of them are available on-line, for example:

  http://www.ctan.org/pub/tex-archive/info/impatient/book.pdf 

\halign is explained on page 178.

BTW, plain TeX is not really cryptic.  Try to understand this code:

  http://www.muppetlabs.com/~breadbox/intercal-man/s02.html

Regards,
  Reinhard

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