Using \def inside mathematical environment

Question

I have the following:

\documentclass{article}
\usepackage{amsmath}
\usepackage{witharrows}
\begin{document}
\def\var{x}
[
    \begin{WithArrows}
        \var\var&=\def\var{y}\var\var\
        \var
    \end{WithArrows}
]
\end{document}

I wanted to change the \var value to y but it only works for the \var immediatly after the \def and on that line.

The result of the compilation is:

And I'm wondering why the \var on the second line is not affected by the instruction above.

@egreg I'm thinking about exercises where you need a change in variable (like solving limits) — Concept7, Jul 21 '20 at 20:21
So losing track of what is what? I'm not sure how this can be helpful. — egreg, Jul 21 '20 at 20:40
@egreg it's understandable that you are not sure how it can be helpful but I am, that's good enough for me. Thank you. — Concept7, Jul 21 '20 at 21:02
@egreg I now see your point and you are correct! I made an exercise resolution and sent it to a friend in a .tex file and he had a lot of difficulties editing it because of commands I used... I still think the idea is good to send the finished product but if I plan on ever sending the .tex it would be problematic. Sorry for being harsh in my previous comment. — Concept7, Jul 22 '20 at 09:43

score 2 · Accepted Answer · answered Jul 21 '20 at 16:04

Change \def to \gdef, to make the definition global. Inside the environment, each subline is its own group, so the \def does not carry over outside of it.

\documentclass{article}
\usepackage{amsmath}
\usepackage{witharrows}
\begin{document}
\def\var{x}
[
    \begin{WithArrows}
        \var\var&=\gdef\var{y}\var\var\
        \var
    \end{WithArrows}
]
\end{document}

Using \def inside mathematical environment

1 Answers1