Differences Between Theorems Modules (AMS and non AMS)

[Jean-Marc Lasgouttes]

Le 15/09/2022 à 14:17, Udicoudco a écrit :
> Hello again,
> 
> I took a look at the Named Theorems Module today, and the LaTeX code
> there seems to be a bit strange. In the preamble of the layout Named
> Theorem there is the following code:
> 
>      \newcommand\thmsname{\protect\theoremname}
>      \newcommand\nm at thmtype{theorem}
>      \theoremstyle{plain}
>      \newtheorem*{namedtheorem}{\thmsname}
>      \newenvironment{namedthm}[1][Undefined Theorem Name]{
>        \ifx{#1}{Undefined Theorem Name}\renewcommand\nm at thmtype{theorem*}
>        \else\renewcommand\thmsname{#1}\renewcommand\nm at thmtype{namedtheorem}
>        \fi
>        \begin{\nm at thmtype}}
>        {\end{\nm at thmtype}}

Hi again Udi,

This module has been proposed in ticket 6279
https://www.lyx.org/trac/ticket/6279

Updating and fixing it would be great. I think that the LabelString 
could be empty, so that it is clear that the argument inset will be used 
as a label. And the default could be set to "theorem", for example.

Feel free to propose a replacement.

JMarc

> 
> \ifx is not really a macro with two arguments, but it is only looking
> at the next two tokens, it compares the token { with the one after it,
> which causing, in this situation, to get always the false output.
> 
> This means that if a user would not give a name via the optional
> argument, the output theorem will have a label "Undefined Theorem
> Name", which I don't think is the preferable outcome (and it might not
> be what the author of the module meant as well).
> 
> In addition, note that if there was a case that the true case was
> happening, the environment theorem* is not defined anywhere in the
> module, which will cause a LaTeX Error: Environment theorem*
> undefined.
> 
> I think it is reasonable to change this module in a way that if the
> optional argument is empty, the output would be a theorem with the
> label "Theorem".
> 
> This way, there is only need for one layout in this module, the Named
> Theorem layout, Since the Theorem* layout defined there would be
> achievable with the Named Theorem with the default optional argument
> (or by setting it to Theorem).
> 
> Also note that every line that does not end with a control word, TeX
> will see a n end-of-line character, hence will add an (what i believe
> to be in this case, an undesired) space (since space after control
> words are ignored). So in the current code, there are also a few extra
> spaces in the environment namedthm.
> 
> Best Regards,
> Udi