557 now I understand your riddle, but assuming they can each anticipate the other’s movements, I don’t have a clue what the answer is, unless the rodef can manipulate the circle.
As for a riddle, an oldy but a goody:
You are in a closed room that has two doors and two other people. One door leads to death, and one leads to life. One person speaks only the truth and one person speaks only lies. You do not know which person is which or which door leads to what. You are allowed to ask one question to either person of your choosing to help you exit through the correct door. What question can you ask to guarantee your survival?
If you’ve already heard this riddle or read the answer elsewhere, please don’t ruin it for others.