Using def inside mathematical environment

Question

I have the following:
documentclass{article}

usepackage{amsmath}
usepackage{witharrows}

begin{document}
    
defvar{x}
    
[
    begin{WithArrows}
        varvar&=defvar{y}varvar
        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.

Steven B. Segletes · Accepted Answer

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}
    
defvar{x}
    
[
    begin{WithArrows}
        varvar&=gdefvar{y}varvar
        var
    end{WithArrows}
]

end{document}

Using def inside mathematical environment

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