Re: [possible patch] Remove the '\\[0pt]' string from the last line of a verse block in LaTeX export

["Juan Manuel Macías" <maciaschain@posteo.net>]

Ihor Radchenko writes:

> Juan Manuel Macías <maciaschain@posteo.net> writes:
>
>> If I'm not mistaken, in TeX '\\' can only be used in horizontal mode:
>> that is, within a paragraph. At the end of an environment like verse
>> (\end{verse}) you are forced to enter vertical mode, and a new paragraph
>> starts.
>
> Is it true for any environment? Or just some?

In principle, nothing prevents one from defining an environment for use
in horizontal mode (within the paragraph). E.g.:

\newenvironment{foo}{\itshape}{}

Lorem \begin{foo}ipsum\end{foo} dolor.

But the usual thing is that the beginning/end of an environment changes to
vertical mode, with \par or something more elaborate.


>> Therefore, I think that whether or not a verse environment ends with \\ is
>> irrelevant to LaTeX. The problem is that when it ends with \\[0pt], for
>> some reason that escapes me, the space after the environment is altered.
>
> I see. Although, I am not 100% if it is something we have to deal with
> in Org mode. May it be better to report this as a bug to LaTeX devs?

hmm... I don't know if this should be considered a bug. We may think
that \\[0pt] should never do anything, but we must keep in mind that the
end of the verse environment is the end of a paragraph, and it changes
to vertical mode. And the end of a paragraph is an illogical place to
put that command. But it seems that it also alters things when it is at
that point. Check out this reply from David Carlisle
(https://tex.stackexchange.com/a/82666):

#+begin_quote
\\ at the end of a paragraph causes bad output with an empty, maximally under-full, box,
and so you get a warning about badness 10000, the visual effect looks a bit like extra
vertical space but it is not: it is an extra spurious line at the end of the paragraph,
and for example it is not dropped at a page break and will break widow/club line
calculations.
#+end_quote

If there are environments that redefine \\, such as verse or tabular,
probably putting the optional argument of \\ with a value of 0pt at the
end of verse alters the calculation of the normal space after the
environment, making it shorter. I think that here we would not have a
LaTeX bug, because the syntax of the verse environment itself says that
the last line should not carry any \\ mark. 

At the end of the tables I have not noticed any side effects. But in the
export of the verse block, I would be in favor of somehow eliminating
that last \\[0pt].

Best regards,

Juan Manuel