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Merge pull request #1360 from ethereum/JustinDrake-patch-23

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Add summaries and expansions to simple-serialize.md
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Danny Ryan 2019-08-14 11:09:28 -06:00 committed by GitHub
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@ -217,6 +217,12 @@ We now define Merkleization `hash_tree_root(value)` of an object `value` recursi
Let `value` be a self-signed container object. The convention is that the signature (e.g. a `"bytes96"` BLS12-381 signature) be the last field of `value`. Further, the signed message for `value` is `signing_root(value) = hash_tree_root(truncate_last(value))` where `truncate_last` truncates the last element of `value`.
## Summaries and expansions
Let `A` be an object derived from another object `B` by replacing some of the (possibly nested) values of `B` by their `hash_tree_root`. We say `A` is a "summary" of `B`, and that `B` is an "expansion" of `A`. Notice `hash_tree_root(A) == hash_tree_root(B)`.
We similarly define "summary types" and "expansion types". For example, [`BeaconBlock`](./core/0_beacon-chain.md#beaconblock) is an expansion type of [`BeaconBlockHeader`](./core/0_beacon-chain.md#beaconblockheader). Notice that objects expand to at most one object of a given expansion type. For example, `BeaconBlockHeader` objects uniquely expand to `BeaconBlock` objects.
## Implementations
| Language | Project | Maintainer | Implementation |