hash identifying the series of blocks that must precede it if the block is to be considered valid. This series of blocks, from the genesis (first) block to the most recent one, is known as the blockchain. Each node connects with a relatively small subset of the network—its "peers". It offers blocks and unvalidated transactions (i.e. transactions not yet in the blockchain) to its peers for download, and it downloads any of these from its peers that it doesn't already have. Its list of unvalidated transactions is known as a "mempool". A node may choose to create a copy of the state for itself. It does this by starting with the genesis state and executing every transaction in the blockchain, in the proper order of blocks and in the order they are listed within each block. Any Ethereum account may "stake" (deposit) 32 ETH to become a validator. At the end of each "epoch" (32 block slots, each lasting 12 seconds), each validator is pseudorandomly assigned to one of the slots of the epoch after the next, either as the block proposer or as an attester. The block proposer creates a block that is intended to become the new "head" (latest block) of the blockchain, and the attesters attest to which block is at the head of the chain. If a validator makes self-contradicting proposals or attestations, or if it is inactive, it loses a portion of its stake. It may add to its stake at any time. A validator's attestation is given a weight equal to its stake or 32, whichever is less. According to the Ethereum protocol, the blockchain with the highest accumulated weight of attestations is the canonical chain. Validators are rewarded for proposing and attesting to blocks that become part of the canonical chain. Ether Ether (ETH) is the cryptocurrency generated in accordance with the Ethereum protocol as a reward to validators in a proof-of-stake system for adding blocks to the blockchain. Ether is represented in the state as an unsigned integer associated with each account, this being the account's ETH balance denominated in wei (1018 wei = 1 ether). At the end of each epoch, new ETH is generated by the addition of protocol-specified amounts to the balances of all validators for that epoch, with the block proposers receiving the largest portion. Additionally, ether is the only currency accepted by the protocol as payment for