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I'm trying to replicate the figure below,can someone help me? the latex code is below

Let $A$ and $B$ be rings, where $B$ is an $A$-module.
If
\[
(a\cdot x)\underset{B}{\cdot}(b\cdot y)=(a\underset{A}{\cdot} b)\cdot(x\underset{B}{\cdot} y),\, \forall a,b\in A\textrm{ and }x,y\in B
\]
then $\phi:A\rightarrow B$ is a ring homomorphism and the structure of $B$ as $A$-module via $\phi$ is the original structure of $B$ as $A$-module.

if I use underset it looks awful.

[enter image description here]

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7
  • 1
    Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
    – JamesT
    Sep 24 at 12:50
  • I need help drawing these arrows explaining where the elements are being operated on.
    – Luiz Claudio Oliveira
    Sep 24 at 12:59
  • similar to this image imagizer.imageshack.com/img924/5787/cZEZi2.png
    – Luiz Claudio Oliveira
    Sep 24 at 12:59
  • Those arrows are all over the place though, do you want them squiggly or straight or what? This is why I put we need more info. Your question, whilst lacking any code, doesn't make it clear
    – JamesT
    Sep 24 at 13:00
  • They're badly made because I made them by hand. The arrow can go either way, I just want to draw an arrow to explain the operation.
    – Luiz Claudio Oliveira
    Sep 24 at 13:14

1 Answer 1

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3

tikzmark on equation

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{tikzmark}
\usepackage{amsmath}
\newcommand{\tmn}{\tikzmarknode}

\begin{document}
    \[
    (a\tmn{A}{\cdot} x)\underset{B}{\cdot}(b\tmn{B}{\cdot} y)=(a\underset{A}{\cdot} b)\tmn{C}{\cdot}(x\underset{B}{\cdot} y),\, \forall a,b\in A\textrm{ and }x,y\in B
    \]
    \begin{tikzpicture}[overlay,remember picture,every path/.style={->}]
        \draw (A) --++ (0,-1) node[below] {Comment 1};
        \draw (B) --++ (0,-2) node[below] {Comment 2};
        \draw (C) --++ (0,-1) node[below] {Comment 3};
    \end{tikzpicture}
\end{document}

As for the decoration (if it's really needed), you may fond by yourself what pleases you the most. Please note that you'll have to compile at least twice to get the final result with tikzmark.

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