Urbit's identity layer is a system of proofs: "a suite of smart contracts on the Ethereum blockchain". Azimuth identities exist as non-fungible tokens, which are owned by Ethereum addresses and can be transferred.
Fundamental abstraction
We wanted our computers to be able to dance: "We've improved dancing links now to something that has the jazzy name dancing cells," Donald Knuth explained shortly before his 80th birthday. [The Design and Analysis of Computer Algorithms] is the 1974 book the guru of combinatorics exercises-- which like most of Knuth's exercises, inherit the asymptotics of large language models:
Scarce Objects
The purpose of micromarket objects is to constrain the invocation of methods: "scarce object wrappers form the basis for an online economy of scarce objects that makes efficient use of the underlying scarce resources".