ABSTRACT
On Sunday Beauty learns she is going to be put to sleep for the next two days, and be woken briefly either once or twice. A fair coin is tossed: if it lands Heads she will be woken just on Monday, if Tails on both Monday and Tuesday. If she is woken just on Monday, she is put back to sleep with a drug that makes her forget that waking. Beauty knows all this, so that when she wakes on Monday she doesn’t know which day it is. On waking, what probability should she assign to the coin having landed Heads?
