title: Using Tikz positioning with \onslide\visible\only inside beamer
body: <p>I have the following image:
  <a href="https://i.stack.imgur.com/EtgrE.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EtgrE.jpg" alt="enter image description here" /></a></p>
  <p>and I want its elements to appear in a certain order in my beamer presentation. For the moment, I'm trying to make a_1, a_2 appear in a second slide. I'm using this code:</p>
  <pre><code>\documentclass{beamer}
  \usepackage{textcomp}
  \usepackage{tikz}
  \usetheme{Madrid}
  \begin{document}
  \begin{frame}{}
   \usetikzlibrary{shapes,arrows, positioning, calc}  
   
  \tikzset{%
    block/.style    = {rounded corners, draw, thick, circle, minimum height = 3em,
      minimum width = 3em, fill = yellow!50},
    point/.style    = {coordinate}, % Input
  }
  \begin{tikzpicture}[auto, thick, node distance=2cm, &gt;=triangle 45]
  %\node[block] (A1) at (0,0) {$A_1$};
  %\node[block, right  = 1cm of A1] (A2) {$A_2$};
  \node[below  = of A1] (a1) {{\visible&lt;2-&gt;{$a_1$}}};
  \node[below  = of A2] (a2) {{\visible&lt;2-&gt;{$a_2$}}};
  \node[below  = of A1] (a1) {$a_1$};
  \node[below  = of A2] (a2) {$a_2$};
  \draw[-&gt;] (A1.south) ++(0,-0.3) -- ++(0, -1.3);
  \draw[-&gt;] (A2.south) ++(0,-0.3) -- ++(0, -1.3);
  \end{tikzpicture}
  \end{frame}
  \end{document}
  </code></pre>
  <p>but all I get is this:</p>
  <p><a href="https://i.stack.imgur.com/CBgp3.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CBgp3.jpg" alt="" /></a></p>
  <p><a href="https://i.stack.imgur.com/AfVLI.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AfVLI.jpg" alt="" /></a></p>
  <p>I get errors like: &quot;unknown arrow tip kind 'triangle 45'&quot; and also &quot;unknown operator 'o' or 'of ' in (of A1).
  It's my first time using Tikz, and I'm not really practical with beamer tools like \onslide, \only or \visible. I think I could create different images, one for each frame, and then add them with \includegraphics and \pause, but it would be more practical if I managed to achieve the same result without creating different pictures. Any help would be really appreciated.</p>