6

Does anyone know how to draw a vertical arrow over a whole proof to demonstrate that the proof goes from the bottom to the top?

My MWE is here:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[czech]{babel}
\usepackage{mathtools,amssymb,amsthm}

\newcommand{\R}{\mathbb{R}}
\DeclarePairedDelimiter{\abs}{|}{|}

\begin{document}
\begin{proof}
    \begin{align*}
    \epsilon \in \R^+: \abs*{\frac{2n-3}{3n-2} - \frac{2}{3}} &< \epsilon \\
    \abs*{\frac{-5}{3(3n-2)}} &< \epsilon \\
    \frac{5}{3} \cdot \frac{1}{\epsilon} &< 3n-2 \\
    n &> \frac{1}{3} \left(\frac{5}{3\epsilon}+2\right)
    \end{align*}
    Tedy tvrzení platí pro skoro všechna $n$ počínaje třeba $n = 
    \frac{1}{3} \left(\frac{5}{3\epsilon}+2\right) + 1.$
\end{proof}
\end{document}

It looks like this and I want to have the vertical arrow there:

proof-with-arrow

Thanks a lot!

1 Answer 1

7

Change your align* into aligned and add \right\Uparrow next to it, with a \left. to balance it.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[czech]{babel}
\usepackage{mathtools,amssymb,amsthm}

\newcommand{\R}{\mathbb{R}}
\DeclarePairedDelimiter{\abs}{|}{|}

\begin{document}

\begin{proof}
\[
\left.
\begin{aligned}
\epsilon \in \R^+: \abs*{\frac{2n-3}{3n-2} - \frac{2}{3}} &< \epsilon \\
\abs*{\frac{-5}{3(3n-2)}} &< \epsilon \\
\frac{5}{3} \cdot \frac{1}{\epsilon} &< 3n-2 \\
n &> \frac{1}{3} \left(\frac{5}{3\epsilon}+2\right)
\end{aligned}
\quad\right\Uparrow
\]
Tedy tvrzení platí pro skoro všechna $n$ počínaje třeba 
$n = \frac{1}{3} \left(\frac{5}{3\epsilon}+2\right) + 1$.
\end{proof}

\end{document}

enter image description here

Now that you know how to do it, add instead some explanatory words before the display and remove the arrow.

2
  • Thanks a lot! You suggest to neaten my question? Can you please explain to me precisely what I should do? Should I remove the second picture? And "add instead some explanatory words before the display" is a little bit vague instruction on editing my post for me, sorry, I'm a little green here xD
    – JoudaBouda
    Feb 14, 2022 at 19:45
  • @JoudaBouda The suggestion is to use words to explain what is shown by the formulas, so the uparrow is not really needed.
    – egreg
    Feb 14, 2022 at 20:20

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