“aux” is the same. And file ending doesn’t matter. Short version: I had this fun experience a few years back. I used cygwin and Vim for coding and used some old compiler for embedded systems. I created a file called “aux.c” in cygwin. No problem. I compiled my code. Got very strange error. Trouble shooted, tested a bunch of things. Wasted lots of hours before I figured out that “aux” was reserved on one abstraction later but not on another, so Vim/cygwin could access it. My dos compiler couldn’t. Fun times.