In the most of current sharded blockchains, there is a second chain required for the computation needed for the maintenance of the whole of the network and receiving updates of the shards and their snapshots. Such a chain has different names in variant protocols: Beacon chain (Ethereum 2.0), Relay chain (PolkaDot) etc.
So the second chain is used for keeping shards snapshots and maintenance of the network.
According to this answer: https://ethereum.stackexchange.com/a/72045/23024 :
Beacon chain validators for a particular shard, randomly get chosen to add the hash of the tip of the shard, to the beacon chain.
Does it mean that a Beacon chain validator CANNOT be a shard validator at the same time?
- If it is NOT permitted, Why?
- If it is permitted, How?