v4: amscd with space between @ and >

[pkra]

Not great authoring and easy to fix but FYI the following

\begin{CD}
A @ > x >> Y
\end{CD}

renders to

Removing the space between @ and > fixes this. But "real" amscd doesn't mind the additional space.

[dpvc]

Thanks, I'll see about making @ handle spaces properly.

[dpvc]

I've made a PR to fix this.