# Bend vertical arrow in commutative diagram in Tikz

I would like the double arrow in the center to be bend. Here is what I have now:

$\begin{tikzcd} \bullet \arrow[bend left=75]{rr}[name=O]{ff'} \arrow[bend right=75]{rr}[name=S,swap]{gg'} \arrow[bend left=50]{r}[name=U]{f} \arrow[bend right=50]{r}[name=D,below]{g} & \bullet \arrow[Rightarrow,to path=(U) -- (D)]{} \arrow[bend left=50]{r}[name=W]{f'} \arrow[bend right=50]{r}[name=E,below]{g'} & \bullet \arrow[Rightarrow,to path=(W) -- (E)]{} \arrow[Rightarrow,to path=(O) -- (S)]{} \end{tikzcd}$


All my attempts have failed.

• Welcome to TeX.SX! A tip: If you indent lines by 4 spaces, they'll be marked as a code sample. You can also highlight the code and click the "code" button (with "{}" on it). Sep 13 '17 at 16:17
• Please make your code compilable (if possible), or at least complete it with \documentclass{...}, the required \usepackage's, \begin{document}, and \end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem. Sep 13 '17 at 16:22

Credits to Gonzalo Medina: https://tex.stackexchange.com/a/50955/101651.

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
Like this?
$\begin{tikzcd} \bullet \arrow[bend left=75]{rr}[name=O]{ff'} \arrow[bend right=75]{rr}[name=S,swap]{gg'} \arrow[bend left=50]{r}[name=U]{f} \arrow[bend right=50]{r}[name=D,below]{g} & \bullet \arrow[Rightarrow, to path=(U) -- (D)]{} \arrow[bend left=50]{r}[name=W]{f'} \arrow[bend right=50]{r}[name=E,below]{g'} & \bullet \arrow[Rightarrow,to path=(W) -- (E)]{} \arrow[Rightarrow,to path={(O) ..controls +(2.5,0.7) and +(2.5,-0.7).. (S)}]{} \end{tikzcd}$
Or like this?
$\begin{tikzcd} \bullet \arrow[bend left=75]{rr}[name=O]{ff'} \arrow[bend right=75]{rr}[name=S,swap]{gg'} \arrow[bend left=50]{r}[name=U]{f} \arrow[bend right=50]{r}[name=D,below]{g} & \bullet \arrow[Rightarrow, to path=(U) -- (D)]{} \arrow[bend left=50]{r}[name=W]{f'} \arrow[bend right=50]{r}[name=E,below]{g'} & \bullet \arrow[Rightarrow,to path=(W) -- (E)]{} \arrow[Rightarrow, shorten >=2pt, shorten <=3pt, to path={(O) ..controls +(.4,-1) and +(.4,1).. (S)}]{} \end{tikzcd}$
\end{document}


• The second one is exactly what I wanted! Thanks a million! Sep 14 '17 at 15:39