I have a diagram of the following form, written with the package amscd
:
\begin{align*}
\begin{CD}
W @>\phi>> X \\
@V{a}V{b}V @V{c}V{d}V \\
Y @>\phi>> Z \\
\end{CD}
\end{align*}
It want the vertical arrows to be parallel arrows in opposite direction, such that a
and c
point downwards and b
and d
point upwards. (For those who understand the terms, it is about an isomorphism between chain complexes.)
To my best knowledge, amscd
does not provide these features. Can you show me a piece of code that provides this functionality and is similarly easy to use?