数学文本上方、下方和周围的箭头？

Question

我正在寻找使用 TikZ 绘制连接普通数学文本片段的标记箭头，如下所示：

Answer 1

TikZ 中的解决方案是将数学表达式的组成部分设置为一系列节点。然后将注释标签放置为节点。最后在节点之间绘制箭头。

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\usepackage{bookman}
\begin{document}
% \[
%   \lambda x.\,(\lambda x.\, x\,y)\,
%   (x\,(\lambda x.\,\lambda y.\,y\,z\,x))
% \]
\[
\begin{tikzpicture}[
  inner sep=0pt,
  outer sep=0pt,
  baseline=(lx_1.base),
]
  \path[every node/.append style={anchor=base west}]
    (0, 0)
    \foreach \name/\code in {
      lx_1/\lambda x,
      tmp/.\,(,
      lx_2/\lambda x,
      tmp/.\,,
      x_1/x,
      tmp/\,,
      y_1/y,
      tmp/)\,(,
      x_2/x,
      tmp/\,(,
      lx_3/\lambda x,
      tmp/.\,,
      ly_1/\lambda y,
      tmp/.\,,
      y_2/y,
      tmp/\,,
      z_1/z,
      tmp/\,,
      x_3/x,
      tmp/))%
    } {
      node (\name) {$\code$}
      (\name.base east)
    }
  ;
  \path[
    every node/.append style={
      anchor=base,
      font=\slshape\scriptsize,
    },
  ]
    % Annotation: frei
    (y_1.base) -- node[above=1.2\baselineskip] (frei) {frei} (z_1)
    % 4 annotations: gebunden
    (lx_1.base) -- node[below=3\baselineskip] (geb_1) {gebunden} (x_2)
    (lx_2.base) -- node[below=1.4\baselineskip] (geb_2) {gebunden} (x_1)
    (lx_3.base) -- node[below=3\baselineskip] (geb_3) {gebunden} (x_3)
    (ly_1.base) -- node[below=1.4\baselineskip] (geb_4) {gebunden} (y_2)
  ;
  \begin{scope}[
    >={Stealth[length=5pt]},
    thick,
    rounded corners=2pt,
    shorten <=.3em,
    shorten >=.3em,
  ]
    \draw[->] (frei) -| (y_1);
    \draw[->] (frei) -| (z_1);
    \def\GebArrow#1#2#3{
      \draw[->]
        (#2.north) ++(0, .3em) coordinate (tmp)
        (#1) |- (tmp) -| (#3)
      ;%
    }
    \GebArrow{x_2}{geb_1}{lx_1}
    \GebArrow{x_1}{geb_2}{lx_2}
    \GebArrow{x_3}{geb_3}{lx_3}
    \GebArrow{y_2}{geb_4}{ly_1}
  \end{scope}
\end{tikzpicture}
\]
\end{document}