  Permission-less blockchains can realise trustless trust, albeit at the cost
of limiting the complexity of computation tasks. To explain the implications
for scalability, we have implemented a trust model for smart contracts,
described as agents in an open multi-agent system. Agent intentions are not
necessarily known and autonomous agents have to be able to make decisions under
risk. The ramifications of these general conditions for scalability are
analysed for Ethereum and then generalised to other current and future
platforms.
