Commutative diagrams
AMScd diagrams must start with a "require":
$\require{AMScd}$ \begin{CD} A @>a>> B\\ @V b V V= @VV c V\\ C @>>d> D \end{CD} to get this diagram: $\require{AMScd}$ \begin{CD} A @>a>> B\\ @V b V V= @VV c V\\ C @>>d> D \end{CD}
@>>> is used for arrow right
@<<< is used for arrow left
@VVV is used for arrow down
@AAA is used for arrow up
@= is used for horizontal double line
@| is used for vertical double line
@. is used for no arrow
Another example:
\begin{CD} A @>>> B @>{\text{very long label}}>> C \\ @. @AAA @| \\ D @= E @<<< F \end{CD} \begin{CD} A @>>> B @>{\text{very long label}}>> C \\ @. @AAA @| \\ D @= E @<<< F \end{CD}
Long labels increase the length of the arrow and in this version also automatically increase corresponding arrows.
$\require{AMScd}$ \begin{CD} RCOHR'SO_3Na @>{\text{Hydrolysis,$\Delta, Dil.HCl$}}>> (RCOR')+NaCl+SO_2+ H_2O \end{CD} $\require{AMScd}$ \begin{CD} \text{RCOHR'SO$_3$Na} @>{\text{Hydrolysis, $\Delta,$ Dil. HCl}}>> \text{(RCOR')+NaCl+SO$_2$+ H$_2$O} \end{CD}
