Non-Fungible Tokens Formalised

Abstract

Non-fungible tokens, NFTs, have been used to record ownership of real estate, art, digital assets, and more recently to serve legal notice. They provide an important and accessible non-financial use of cryptocurrency's blockchain but are peculiar because ownership by NFT confers no rights over the asset. This work shows that it is possible to specify and reason about that peculiar property by combining functional and epistemic conditions. Suitability of the specification is demonstrated by (a) proof that the blockchain implementation conforms to it, and (b) its aptitude in analysing NFT's recent use in serving legal notice.