[tex-k] Possible error in The TeXbook Chapter 24

[Kim Young Min]

Sorry, my mistake. You're right. I thought `true` can be repeating for
some reason.

As <optional spaces> appear in both cases, the syntax could be

> <normal dimen>\is<internal dimen>\alt<factor><optional spaces><unit of
measure>
> <unit of measure>\is<internal unit>
> \alt<optional {\tt true}><physical unit><one optional space>
> <optional {\tt true}>\is[true]<optional spaces>\alt<empty>

Regards,
Young Min Kim

On Sun, Oct 27, 2019 at 4:25 PM Julian Gilbey <julian at d-and-j.net> wrote:

> On Thu, Oct 24, 2019 at 05:08:39PM -0600, Karl Berry wrote:
> >     So the formal syntax for <optional true> should be:
> >
> >     > <optional {\tt true}>\is<optional spaces>
> >     >   \alt<optional {\tt true}>[true]<optional spaces>
> >
> > I think you are right. I will put on the pile for Don's next review (in
> > 2021). Thanks!
>
> I think there's a typo here, as that would allow the impermissible
> "truetrue".
>
> Rather, the following appears to be the correct replacement:
>   <optional {\tt true}>\is<optional spaces>
>     \alt<optional spaces>[true]<optional spaces>
>
> Best wishes,
>
>    Julian
>
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