4,424 research outputs found
A Concurrent Perspective on Smart Contracts
In this paper, we explore remarkable similarities between multi-transactional
behaviors of smart contracts in cryptocurrencies such as Ethereum and classical
problems of shared-memory concurrency. We examine two real-world examples from
the Ethereum blockchain and analyzing how they are vulnerable to bugs that are
closely reminiscent to those that often occur in traditional concurrent
programs. We then elaborate on the relation between observable contract
behaviors and well-studied concurrency topics, such as atomicity, interference,
synchronization, and resource ownership. The described
contracts-as-concurrent-objects analogy provides deeper understanding of
potential threats for smart contracts, indicate better engineering practices,
and enable applications of existing state-of-the-art formal verification
techniques.Comment: 15 page
Long Nonbinary Codes Exceeding the Gilbert - Varshamov Bound for any Fixed Distance
Let A(q,n,d) denote the maximum size of a q-ary code of length n and distance
d. We study the minimum asymptotic redundancy \rho(q,n,d)=n-log_q A(q,n,d) as n
grows while q and d are fixed. For any d and q<=d-1, long algebraic codes are
designed that improve on the BCH codes and have the lowest asymptotic
redundancy \rho(q,n,d) <= ((d-3)+1/(d-2)) log_q n known to date. Prior to this
work, codes of fixed distance that asymptotically surpass BCH codes and the
Gilbert-Varshamov bound were designed only for distances 4,5 and 6.Comment: Submitted to IEEE Trans. on Info. Theor
Fake projective planes, automorphic forms, exceptional collections
On the projective plane there is a unique cubic root of the canonical bundle
and this root is acyclic. On fake projective planes such root exists and is
unique if there are no 3-torsion divisors (and usually exists, but not unique,
otherwise). Earlier we conjectured that any such cubic root must be acyclic. In
the present note we give two short proofs of this statement and show acyclicity
of some other line bundles on the fake projective planes with at least
automorphisms. Similarly to our earlier work we employ simple representation
theory for non-abelian finite groups. The novelty stems from the idea that if
some line bundle is non-linearizable with respect to a finite abelian group,
then it should be linearized by a finite, \emph{non-abelian}, Heisenberg group.
For the second proof, we also demonstrate vanishing of odd Betti numbers for a
class of abelian covers, and use a linearization of an auxiliary line bundle as
well.Comment: 13 pages; completely reorganized, title changed, references expande
Copper-Catalyzed Arylation of 1\u3cem\u3eH\u3c/em\u3e-Perfluoroalkanes
A general method has been developed for arylation of readily available 1H-perfluoroalkanes. The method employs aryl iodide and 1H-perfluoroalkane reagents, DMPU solvent, TMP2Zn base, and a copper chloride/phenanthroline catalyst. Preliminary mechanistic studies are reported
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