I have a Raspberry Pi (but that should be immaterial) to which, normally, connect:


a USB hard drive
a SD card adapter.


I've been getting inconsistent device names. Sometimes the hard drive shows up at /dev/sda, and the card reader as /dev/sdb. Today, for reasons unknown (to me), the hard drive is a /dev/sde, and the card reader is at /dev/sda. There aren't any other disk-like devices.

How do I make those consistent, without having to become a UDEV expert, preferably? :-)

Added: This is Arch Linux with systemd and built-in UDEV.


Question: does every right-angled coxeter group have a right-angled artin group as a subgroup of finite index?
Answer: As James points out, the paper of Davis and Januskiewicz proves the inverse.  To see that the answer to your question is 'no', consider the right-angled Coxeter group whose nerve graph is a pentagon.  That is, it's the group with presentation
$\langle a_1,\ldots, a_5 \mid a_i^2=1, [a_i,a_{i+1}]=1\rangle$
where the indices are considered mod 5.

This group acts properly discontinuously and cocompactly on the hyperbolic plane, and it's not hard to see that it has a finite-index subgroup which is the fundamental group of a closed hyperbolic surface.  Every finite-index subgroup of a right-angled Artin group is either free or contains a copy of $\mathbb{Z}^2$, but the fundamental group of a closed hyperbolic surface has no finite-index subgroups of this form.