在图表中间添加箭头标签

Question

我有下面的图片，但我希望中间箭头的标签 $\tilde{f}$ 位于通过幻影箭头定义路径后添加的箭头的顶部。

有什么办法可以做到这一点？

% !TEX TS-program = XeLaTeX
\documentclass[draft]{article}
\usepackage{tikz-cd}
\usetikzlibrary{arrows}
\usetikzlibrary{decorations.markings,intersections}


\begin{document}

   \tikzset{%
    scalearrow/.style n args={3}{
     decoration={
      markings,
       mark=at position (1-#1)/2*\pgfdecoratedpathlength
         with {\coordinate (#2);},
       mark=at position (1+#1)/2*\pgfdecoratedpathlength
        with {\coordinate (#3);},
       },
     postaction=decorate,
     } 
    }

\begin{tikzcd}
{ } &{} &{Set} &{}  \\
{ } &{} &{\tilde{f}} &{}  \\
{A}  \ar[uurr,"!"] \ar[rrr,"f"']  \ar[rrr, shift left=5ex, phantom, scalearrow={0.1}{start}{end}] \ar[to path=(start) --(end), Rightarrow]  &{} &{}  &{B} \ar[uul, "\tilde{L}f"']&{}  \\
\end{tikzcd}



\end{document}  

Answer 1

但上面的图像是作为纯 TikZ 图片绘制的：

\documentclass[tikz, margin=3mm]{standalone}
\usetikzlibrary{positioning,
                quotes}

\begin{document}
\begin{tikzpicture}[
    node distance = 24mm and 12 mm
                    ]
\node (a) {$A$};
\node (s) [above right=of a] {Set};
\node (b) [below right=of s] {$B$};
%
\draw[->]   (a) edge ["!"] (s)
            (b) edge ["$\tilde{L}f$" '] (s)
            (a) edge ["$f$"] (b);
%            
\node (f) [below=9mm of s]  {$\stackrel{\tilde{f}}{\Rightarrow}$};
\end{tikzpicture}
\end{document} 

或者使用Longrightarrow代替Rightarrow：

最后加上tikz-cd：

\documentclass[draft]{article}
\usepackage{tikz-cd}

\begin{document}  
\begin{tikzcd}
    &   &   \mathrm{Set}                            &   \\
    &   &   \stackrel{\tilde{f}}{\Longrightarrow}   &   \\
A  \ar[uurr,"!"] \ar[rrr,"f"']  
    &   &   &   B \ar[uul, "\tilde{L}f"']&{}            \\
\end{tikzcd}
\end{document}