# [texhax] large forward slash

Axel E. Retif axel.retif at mac.com
Tue Feb 10 09:46:49 CET 2009

On  9 Feb, 2009, at 23:12, Pierre MacKay wrote:

> Reinhard Kotucha wrote:
>
>> [...]
>> The reason that \middle is not mentioned in any manual except the
>> e-TeX manual itself is that most people are not aware that all
>> engines
>> are using e-TeX now.  As far as I remember, it was David Kastrup who
>> asked for integrating e-TeX into LaTeX.  He had been interested in
>> the
>> advanced debugging functions provided by e-TeX in the first place.
>> Everything happened in the background, hence it's no wonder that most
>> people are not aware of the "new" features.
>
> Is it really true that \middle is unknown to plain TeX.  I find that
> hard to believe, because I know that I have used it to create some
> non-mathematical displays. I also know that I did not use e-TeX

You *did* use e-TeX (or rather, plain pdfTeX). Try with the example
Reinhard Kotucha is referring to (adapted from the original LaTeX):

$$H = P_{\hbox{ring}} \times \left( -\log_2 ( P_{\hbox{ring}}) \middle) + P_{\hbox{silent}} \times \middle( -\log_2 ( P_{\hbox{silent}}) \right)$$
\bye

If you *really* use TeX (not pdfTeX) you'll get

! Undefined control sequence.
l.3 ...\left( -\log_2 ( P_{\hbox{ring}})   \middle
)

Now try the same with pdfTeX and everything will typeset OK.

Best,

Axel