simplify justificatio/finality notes at genesis

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Danny Ryan 2019-05-06 09:09:37 -06:00 committed by GitHub
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@ -106,4 +106,4 @@ def lmd_ghost(store: Store, start_state: BeaconState, start_block: BeaconBlock)
### Justification and finality at genesis
Clients may choose to refer to the justification and finality data in a given `BeaconState` to determine the finalized/justified head. During the early epochs right after genesis, the justification and finality data are not stored in the `BeaconState`. In their place are "empty" values; for example, the 32-byte zero value as the `finalized_root`. Clients wishing to compute the fork choice in these early epochs should work around this fact of the `BeaconState` to recognize that the genesis epoch and root of the genesis block are _both_ the finalized and justified heads until updated via the state transition function defined in [Phase 0 -- The Beacon Chain](./0_beacon-chain.md). Solutions will be language-specific but one possibility is to treat the zero-value hash as an exceptional case that references the genesis block/epoch.
During genesis, justification and finality root fields within the `BeaconState` reference `ZERO_HASH` rather than a known block. `ZERO_HASH` in `previous_justified_root`, `current_justified_root`, and `finalized_root` should be considered as an alias to the root of the genesis block.