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{\Huge
creates ...
\begin{equation*}
\begin{CD}
{\Bbb R^2} @>F>> {\Bbb R^2} \\
@VhVV @VVkV \\
{\Bbb R^2} @>>G> {\Bbb R^2}
\end{CD}
\end{equation*}
}
{\Huge
\begin{equation*}
\begin{CD}
{\Bbb R^2} @>>F> {\Bbb R^2} @>>H> {\Bbb R^2} @>I>> {\Bbb R^2} \\
@VVhV @VkVV \\
{\Bbb R^2} @>G>> {\Bbb R^2}
\end{CD}
\end{equation*}
}