Changing the definition of "\mod" in spanish impossible?

Question

I'm writing a math text in spanish and want to change the definition of the "\mod" command. However, this seems impossible, as the following MWE shows:

\documentclass{article}

\usepackage[utf8]{inputenc}
\usepackage[spanish]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsmath}

\renewcommand{\mod}{\operatorname{changed}}

\begin{document}
$a \equiv b \mod c$
\end{document}

This produces the following output:

However, if I comment the line

\usepackage[spanish]{babel}

in the above code, the result I get is

as I would expect.

The same phenomenon happens with other math operators that carry accents in spanish, like for example "\max" or "\lim", but it works for such that don't have accents, like "\sin".

Answer 1

I guess that your aim is to use the standard unaccented operator names.

The trick is explained it the manual for babel-spanish, section 5.5.

\documentclass{article}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[spanish]{babel}
\usepackage{amsmath}

% no accents in math operators
\unaccentedoperators

\begin{document}

$a \equiv b \mod{c}$

$\lim_{x\to c}f(x)$

$\arcsin t$

$\max A-\min A$

\end{document}

Beware that \mod is not defined with \operatorname and your proposed redefinition would be bad anyway.

Anyway, here's a correct way to proceed:

\documentclass{article}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[spanish]{babel}
\usepackage{amsmath}

%\unaccentedoperators

\makeatletter
\addto\mathspanish{\renewcommand{\mod}{\operatorname{m\es@op@ac od}}}
\makeatother

\begin{document}

$a \equiv b \mod c$

\end{document}

If you don't want the accent irrespective of \accentedoperators or \unaccentedoperators, remove the \es@op@ac command.

In general, I don't recommend redefining some standard command to do different things (apart from printing just a different symbol). Better defining \omod or whatever name you prefer.