We could use diagonal arrows for the odd-numbered diagrams:

- \searrow produces an arrow pointing to south east \$$\searrow\$$
- \swarrow produces an arrow pointing to south west \$$\swarrow\$$
- \nearrow produces an arrow pointing to north east \$$\nearrow\$$
- \nwarrow produces an arrow pointing to north west \$$\nwarrow\$$

The commuting triangle example would look like this:

$\begin{matrix} X & \xrightarrow{f} & Y \\\\ & \searrow & \downarrow \\\\ & & Z \end{matrix}$

Unfortunately, I don't know of an easy and nice way of labelling the diagonal arrows; maybe we can draw some inspiration from [this Maths Stackexchange thread](https://math.meta.stackexchange.com/questions/2324/how-to-draw-a-commutative-diagram).