ok, this just came to me:
if they agree to only flip the left switch, for example, until someone goes for the second time; then he flips the other switch. they continue to swith that switch until a second person goes twice. then he goes back to flipping the first switch. etc.… they could count the number of times they have reversed. when they get to 23, they would know that they all have gone once.
have I missed something?


formerly known as etaoin...