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I am trying to draw the following picture using tikzcdenter image description here and here is my current attempt:

\begin{document}
    \begin{tikzcd}[row sep=huge, column sep=huge]
    % drawing 0- and 1-celss
    \mathcal{C}  \arrow[dr, "\mathcal{F}"', ""{name=F}]
    \arrow[rr, "\mathcal{H}", ""{name=H, below}] &&
    \mathcal{E} \\
    & \mathcal{D} \arrow[ur, swap, dashed, "\operatorname{Lan}_{\mathcal{F}}\mathcal{H}", ""{name=Lan, above}]
    %
    % drawing 2-cells  
    \arrow[Rightarrow, from=H, to=Lan, "\eta"]
    \end{tikzcd}
\end{document}

However, I cannot get the middle "double arrow" as in the above picture. How can I fix this in the current code?

1 Answer 1

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You can define an alias to define the target. This has the advantage over using the row and column indices that it will still work when you extend the diagram.

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz-cd}
\begin{document} 
\begin{tikzcd}[row sep=huge, column sep=huge] 
 % drawing 0- and 1-celss 
 \mathcal{C} \arrow[dr, "\mathcal{F}"'{name=F}] 
 \arrow[rr, "\mathcal{H}", ""{name=H, below}] && \mathcal{E} \\ 
 & |[alias=D]| \mathcal{D} \arrow[ur, swap, dashed,
 "\operatorname{Lan}_{\mathcal{F}}\mathcal{H}"] 
 % % drawing 2-cells
 \arrow[Rightarrow, from=H, to=D, "\eta",shorten >=1em,shorten <=1em] 
\end{tikzcd} 
\end{document}

enter image description here

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