In accordance with the infinite sharding (ISP) paradigm, each account is considered to be in a separate "accountchain", and the (virtual) blocks of these accountchains will be grouped into shardchain blocks to improve efficiency. In particular, the state of a shardchain is, roughly speaking, the state of all its accountchains. Similarly, a shardchain block essentially consists of a collection of virtual "blocks" of some accounts assigned to a given shardchain. Thus, we get a large number of "account-chains", each of which describes a change in the state of only one account. Also, account-chains send messages to each other to transfer data.