Refinement Calculus of Reactive Systems

Refinement calculus is a powerful and expressive tool for reasoning about sequential programs in a compositional manner. In this paper we present an extension of refinement calculus for reactive systems. Refinement calculus is based on monotonic predicate transformers, which transform sets of post-states into sets of pre-states. To model reactive systems, we introduce monotonic property transformers, which transform sets of output traces into sets of input traces. We show how to model in this semantics refinement, sequential composition, demonic choice, and other semantic operations on reactive systems. We use primarily higher order logic to express our results, but we also show how property transformers can be defined using other formalisms more amenable to automation, such as linear temporal logic (suitable for specifications) and symbolic transition systems (suitable for implementations). Finally, we show how this framework generalizes previous work on relational interfaces so as to be able to express systems with infinite behaviors and liveness properties

Keeping the promise of global accounting standards

Accounting provides a fundamental underpinning for capital markets, and the worldwide spread of International Financial Reporting Standards (IFRS) marks one of the most advanced attempts to develop globally consistent financial rules. The financial crisis has generated heated debate on the economic role of fair-value accounting and other IFRS principles. Underlying these controversies are differing views about the mission and governance of accounting standard-setters, and how standards interact with other public policy instruments. Choices are made more difficult by the absence of relevant precedents for the unique institutional features of the global standard-setting organisation, the IFRS Foundation.

Keeping the Promise of Global Accounting Standards

In this Policy Brief, PIIE Visiting Fellow Nicolas Véron provides a comprehensive analysis of the strategic challenges facing the attempt to harmonize the world's accounting practices through the global spread of International Financial Reporting Standards (IFRS). After taking stock of the initial successes of IFRS adoption, he identifies unsustainable features in the current governance framework of the IFRS Foundation, the organization that hosts IFRS standard-setting, and advocates reform to make the IFRS Foundation accountable not only to individual governments but also to the global investor community. He also proposes a variety of incentives for individual jurisdictions to converge towards IFRS, as such convergence looks set to be more gradual than had been envisaged by the IFRS Foundation in the past.

Instantaneous Decentralized Poker

We present efficient protocols for amortized secure multiparty computation with penalties and secure cash distribution, of which poker is a prime example. Our protocols have an initial phase where the parties interact with a cryptocurrency network, that then enables them to interact only among themselves over the course of playing many poker games in which money changes hands. The high efficiency of our protocols is achieved by harnessing the power of stateful contracts. Compared to the limited expressive power of Bitcoin scripts, stateful contracts enable richer forms of interaction between standard secure computation and a cryptocurrency. We formalize the stateful contract model and the security notions that our protocols accomplish, and provide proofs using the simulation paradigm. Moreover, we provide a reference implementation in Ethereum/Solidity for the stateful contracts that our protocols are based on. We also adopt our off-chain cash distribution protocols to the special case of stateful duplex micropayment channels, which are of independent interest. In comparison to Bitcoin based payment channels, our duplex channel implementation is more efficient and has additional features