  We conduct a systematic study on the light client of permissionless
blockchains, in the setting where the full nodes and the light clients are
rational. Under such a game-theoretic model, we design a superlight-client
protocol to enable a client to employ some relaying full nodes (e.g. two or
one) to read the blockchain. The protocol is "generic", i.e., it can be
deployed disregarding the underlying consensuses, and also "superlight", i.e.,
the computational cost of the light client to predicate the (non)existence of a
transaction in the blockchain becomes a small constant. Since our protocol
resolves a fundamental challenge of broadening the usage of blockchain
technology, it captures a wide variety of important use-cases such as
multi-chain wallets, DApp browsers and more.
