I haven't been able to find detailed instructions on how to use `\compositemap` from the 2cell feature of xypic, and I want to make (relatively simple) pasting diagrams. In particular, I want to typeset the *whiskering* operation, where we have a diagonal double arrow between vertices of a commutative square.

Also, is there a way to reverse the direction of the double arrow in 2cells in xypic, in LyX?

![enter image description here](https://i.stack.imgur.com/4Relr.png)

Heeelp!