TikZ-Arrows – How to Draw Two Arrows Above Each Other in LaTeX

Question

Here is the figure I want to draw:

My big problem is the two arrows above each other with something written above and below. I tried the following:

\documentclass{book}
\begin{document}
\[\begin{tikzcd}
    & \bullet & \bullet \\
    \bullet & \bullet & \bullet
    \arrow[from=2-1, to=2-2]
    \arrow[from=2-2, to=2-3]
    \arrow[from=1-2, to=1-3]
\end{tikzcd}\]
\end{document}

But it did not quite produce what I want.

Answer 1

Use the functionalities of tikz-cd:

    \documentclass{book}
    \usepackage{tikz-cd}

    \begin{document}

    \[\begin{tikzcd}
       E \rar & \prod\limits_\alpha D_\alpha \arrow[r, shift left=0.75ex, "c"] \arrow[r, shift right=0.75ex, "d", swap] & \prod\limits_f D_{c(f)}
    \end{tikzcd}\]

    \end{document}