No equation here: Silver et al. (2018), arXiv:1712.01815, says only that the (s, pi, z) triples are stored and sampled uniformly from the most recent games. What this contributes is a canonical encoding, so the same buffer always yields the same bytes and the same digest whichever language wrote it. The digest is a Rabin-Karp polynomial hash, h <- (131 h + c) mod (2^31 - 1), exact in double precision because every intermediate stays below 2^53. It is not a cryptographic hash and is not presented as one. Writing to disk is opt-in; by default nothing touches the filesystem.