Unpredictability before the block; immutability after it. The hash can tell you four things: not-before, not-after, what order, which one. The hash is not hidden before the block. It does not exist. Anything that contains the hash was made after the hash.
A photograph that contains this morning's block hash was taken after this morning. A signature over the block hash is alive. The hostage holds a newspaper and the headline is the block hash: alive after that block.
The hash is given. Now something can be placed in the timechain. The added data's hash is folded with the ten thousand things into a single commitment; the commitment lands in a block, and now the data provably existed before that block.
Quote block A inside the data: commit the data before block B. Sealed. Made after A, existing before B. No earlier and no later.
Revision is a double-spend of meaning, and the chain refuses it the same way and for the same reason. Order. Earliest counts. And lateness is a verdict.
A number nobody chose and nobody can rig: the hash is a coin the whole world flips at once. Commit to the rule before block A -- audit the rows where sha256(row||hash) falls under the threshold, select the juror, break the tie -- and let A pick. No one can rig a draw that does not exist yet, but a miner can discard an unfavorable block, at the cost of the block reward. Roughly 3.1 BTC of adversary interest. More blocks, a delay function, more ICE.
Four verbs. I was here, no earlier and no later. Sealed.
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