Each node from the list Ej can be selected as part of an optimally dimensioned consensus group (in terms of security and communication), by a deterministic function, based on the randomness source added to the previous block, the round r and a set of variation parameters. The random number, known to all shard nodes through gossip, cannot be predicted before the block is actually signed by the previous consensus group. This property makes it a good source of randomness and prevents highly adaptive malicious attacks. We define a selection function to return the set of chosen nodes (consensus group) Nchosen with the first being the block proposer, that takes following parameters: E, r and sigr−1 - the previous block signature