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

[Julian Gilbey]

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