How to exit lr-mame2003?

My Picade arrived yesterday, was up all night assembling it with RetroPie 4.2, and then was happily playing an old favourite, Nemesis, in lr-mame2003 :)

One question is how I exit the emulator once I’m done playing a game? I’m guessing there’s a key binding in /opt/retropie/configs/all/retroarch.cfg but I’m struggling to figure out what!

Digging around the retroarch menus I hit upon the solution by pressing both the 1-up and coin buttons to set the exit keypress…