Problems with language local math operators

[eg9]

Languages such as Spanish, Ukrainian, Russian and perhaps some more define “language local” math operators due to national mathematical traditions.

For instance they all define (in different ways) \tg for the tangent function, with the consequence that

\documentclass{article}
\usepackage[ukrainian,spanish]{babel}
\usepackage{amsmath}
\begin{document}
Test
\end{document}

fails when the \AtBeginDocument code of ukraineb.ldf tries to do \DeclareMathOperator{\tg}{tg}, because spanish.ldf defines it at the outer level. The error doesn't occur when amsmath is not loaded, because in that case russianb.ldf does \DeclareRobustCommand{\tg}{...}. However, this only shifts the issue, because the definition for Ukrainian overrides the one for Spanish. With previous versions of ukraineb.ldf, it would be Spanish to get over, because ukraineb.ldf didn't do the definitions at begin document. Source: https://tex.stackexchange.com/q/672982/4427

In a bilingual Spanish/Ukrainian document using math, it would be funny to have “lím” for a limit in a Ukrainian language part.¹ Such “localizations” should really be part of the language settings, done in \extras<language> maybe with the possibility of importing them at the outer level, if needed and safe (this depends on the loaded languages).

In any case, within the current state of babel it's impossible to make a Spanish/Ukrainian document.²

_{Footnotes.
¹ In my opinion, Spanish should not use accents in math operators, which are symbols from abbreviations of Latin words, not Spanish ones. But I know that going against tradition is hard.
² The same holds for Russian instead of Ukrainian.}

[jbezos]

Actually, with spanish they already are language dependent, and the manual explains how to disable them (with a @-command, which is admittedly clumsy, but there it is), so it’s certainly possible to make a Spanish/Ukrainian document, although not without some action from the user, which isn’t good.

Note russian is supported here: https://github.com/kia999/babel-russian. As to Ukrainian, I’m not sure if it’s supported.

I’ll investigate if there is something wrong in the babel core.

[ivankokan]

Something that bothered me as well: https://tex.stackexchange.com/questions/611161/different-behavior-of-gcd-analogs-within-babel-russian-and-serbianc.

I think locales' authors must be driven, pushed and encouraged to reach certain level of consistency.

[jbezos]

@ivankokan Definitely.

I’ll report it to the maintainer of the russian style, because it also bombs if the user defines their own \tg in the preamble. I think, like @eg9, they must be language dependent (as in spanish and serbianc [edit: with serbianc sometimes are global and sometimes are local]) or, at least and if done globally, activated only if the language is the main one.

In the case of spanish, there is a workaround:

\documentclass{article}

\usepackage[T2A, T1]{fontenc}
\usepackage[ukrainian,spanish]{babel}

\let\savemathspanish\mathspanish
\let\mathspanish\relax
\AtBeginDocument{%
  \let\mathspanish\savemathspanish
  \selectlanguage{spanish}}

\usepackage{amsmath}

\begin{document}

$\lim\tg$ \foreignlanguage{ukrainian}{$\lim\tg$} $\lim\tg$ 

\end{document}

It prints “lím tg lim tg lím tg”.

But with serbianc it’s not so easy, because the ‘switcher’ isn’t isolated from the rest of \extras....

[ivankokan]

TBH, I have always missed some indication/example of a properly made ldf.

Multiscript languages seem to be good candidates for such thing, is there any 100%-perfect?

[jbezos]

I expanded the corresponding section in the manual a long ago (§ 3) with several recommendations, but perhaps not comprehensive enough.

[jbezos]

Here is a workaround for serbianc:

\documentclass{article}

\usepackage[T2A, T1]{fontenc}
\usepackage[ukrainian,serbianc]{babel}

\AddBabelHook[serbianc]{fix-ops}{afterextras}{%
  \let\sh\relax
  \let\ch\relax
  \let\tg\relax
  \let\ctg\relax
  \let\arctg\relax
  \let\arcctg\relax
  \let\cth\relax
  \let\cosec\relax}
\AtBeginDocument{\DisableBabelHook{fix-ops}}

\usepackage{amsmath}

\begin{document}

$\lim\tg$ \foreignlanguage{ukrainian}{$\lim\tg$} $\lim\tg$ 

\end{document}

Actually, this applies the definitions for Ukrainian, but they are similar. If they were different, they would have to be saved in afterextras and restored in \AtBeginDocument.

[jbezos]

I’m closing this issue because the maintainer of russian and the maintainer of ukrainian have been informed.