$\require{AMScd} \begin{CD} A @>{f}>> B\\ @V{gg}VV {\large\circlearrowleft} @VV{hh}V\\ C @>>{k}> D \end{CD}$

\require{AMScd}
\begin{CD}
A @>{f}>> B\\
@V{gg}VV {\large\circlearrowleft} @VV{hh}V\\
C @>>{k}> D
\end{CD}