A finite simulation method in a non-deterministic call-by-need calculus with letrec, constructors and case

The paper proposes a variation of simulation for checking and proving contextual equivalence in a non-deterministic call-by-need lambda-calculus with constructors, case, seq, and a letrec with cyclic dependencies. It also proposes a novel method to prove its correctness. The calculus' semantics is based on a small-step rewrite semantics and on may-convergence. The cyclic nature of letrec bindings, as well as non-determinism, makes known approaches to prove that simulation implies contextual equivalence, such as Howe's proof technique, inapplicable in this setting. The basic technique for the simulation as well as the correctness proof is called pre-evaluation, which computes a set of answers for every closed expression. If simulation succeeds in finite computation depth, then it is guaranteed to show contextual preorder of expressions

Simulation in the call-by-need lambda-calculus with letrec

This paper shows the equivalence of applicative similarity and contextual approximation, and hence also of bisimilarity and contextual equivalence, in the deterministic call-by-need lambda calculus with letrec. Bisimilarity simplifies equivalence proofs in the calculus and opens a way for more convenient correctness proofs for program transformations. Although this property may be a natural one to expect, to the best of our knowledge, this paper is the first one providing a proof. The proof technique is to transfer the contextual approximation into Abramsky's lazy lambda calculus by a fully abstract and surjective translation. This also shows that the natural embedding of Abramsky's lazy lambda calculus into the call-by-need lambda calculus with letrec is an isomorphism between the respective term-models.We show that the equivalence property proven in this paper transfers to a call-by-need letrec calculus developed by Ariola and Felleisen

Counterexamples to simulation in non-deterministic call-by-need lambda-calculi with letrec

This note shows that in non-deterministic extended lambda calculi with letrec, the tool of applicative (bi)simulation is in general not usable for contextual equivalence, by giving a counterexample adapted from data flow analysis. It also shown that there is a flaw in a lemma and a theorem concerning finite simulation in a conference paper by the first two authors

Simulation in the Call-by-Need Lambda-Calculus with Letrec, Case, Constructors, and Seq

This paper shows equivalence of several versions of applicative similarity and contextual approximation, and hence also of applicative bisimilarity and contextual equivalence, in LR, the deterministic call-by-need lambda calculus with letrec extended by data constructors, case-expressions and Haskell's seq-operator. LR models an untyped version of the core language of Haskell. The use of bisimilarities simplifies equivalence proofs in calculi and opens a way for more convenient correctness proofs for program transformations. The proof is by a fully abstract and surjective transfer into a call-by-name calculus, which is an extension of Abramsky's lazy lambda calculus. In the latter calculus equivalence of our similarities and contextual approximation can be shown by Howe's method. Similarity is transferred back to LR on the basis of an inductively defined similarity. The translation from the call-by-need letrec calculus into the extended call-by-name lambda calculus is the composition of two translations. The first translation replaces the call-by-need strategy by a call-by-name strategy and its correctness is shown by exploiting infinite trees which emerge by unfolding the letrec expressions. The second translation encodes letrec-expressions by using multi-fixpoint combinators and its correctness is shown syntactically by comparing reductions of both calculi. A further result of this paper is an isomorphism between the mentioned calculi, which is also an identity on letrec-free expressions.Comment: 50 pages, 11 figure

Post-outburst spectra of a stellar-merger remnant of V1309 Scorpii: from a twin of V838 Monocerotis to a clone of V4332 Sagittarii

We present optical and infrared spectroscopy of V1309 Sco, an object that erupted in 2008 in a stellar-merger event. During the outburst, V1309 Sco displayed characteristics typical of red transients, a class of objects similar to V838 Mon. Our observations were obtained in 2009 and 2012, i.e. months and years after the eruption of V1309 Sco, and illustrate severe changes in the remnant, mainly in its circumstellar surroundings. In addition to atomic gas observed in earlier epochs, we identified molecular bands of TiO, VO, H$_2$O, ScO, AlO, and CrO. The infrared bands of CrO we analyse are the first astronomical identification of the features. Over the whole period covered by our data, the remnant was associated with a cool ($\lesssim$1000 K) outflow with a terminal velocity of about 200 km/s. Signatures of warmer atomic gas, likely to be still dissipating the energy of the 2008 outburst, dramatically decreased their brightness between 2009 and 2012. In addition, the source of optical continuum disappeared sometime before 2012, likely owing to the formation of new dust. The final stage of V1309 Sco's evolution captured by our spectra is an object remarkably similar to an older red transient, V4332 Sgr. In addition to providing a detailed view on the settling of the eruptive object, the observations presented here reinforce the conclusion that all the Galactic red transients are a manifestation of the same phenomenon, i.e. a stellar merger. The late spectra of V1309 Sco also suggest peculiarities in the chemical composition of the remnant, which still need to be explored.Comment: to appear in A&

Institutional corruption in Russian universities

Russia is about to become an academic superpower, which makes it very successful at least in the context of the BRIC countries—Brazil, Russia, India, China. After various effective reforms, including the Bologna process and the modernization of admissions procedures, the Russian government is now working hard on remedying corruption in higher education

Hunger in Maine

Hunger and food insecurity is on the rise in Maine. Mainers are experiencing a food emergency made graver by the economic recession and rising health costs. The authors of this article discuss hunger in Maine, focusing on private efforts to alleviate it

Managing Business Corruption: Targeting Non-Compliant Practices in Systemically Corrupt Environments

This article focuses on strategies of ‘managing business corruption’ at the firm level and offers insights for practitioners in systemically corrupt environments. Our study of 110 CEOs and owners of companies operating in Russia tested a new, ethnographic approach to managing corruption at a firm level. We conceptualize ‘managing business corruption’ as devising and implementing strategies that mitigate corruption-related risks in an effective way. We argue that such strategies have to target specific non-compliant practices, identified bottom-up, yet also amount to a pragmatic, problem-solving framework at the firm level, implemented top-down. Leadership is a key factor which defines effectiveness of corruption management in systemically corrupt environments. While the latter are generally conducive to tolerance and passive attitudes to corruption among business leaders, we identify proactive modes (preventive and controlling) and possible channels (formal hierarchy and informal networks) for leadership action. The proposed approach can also be used for leadership training

An experimental evaluation of an anti-corruption intervention among Ukrainian university students

In this paper, we investigate experimentally the effect of an anti-corruption intervention -an info folder based on materials developed by Transparency International- on Ukrainian university students’ willingness to participate in an anti-corruption campaign and their general attitude toward corruption. In a survey of 600 students in the Ukrainian city of Lviv, individuals were randomly exposed to either the anti-corruption folder (treatment group) or a folder with information about Lviv (control group). The results suggest that students who have previous experience with bribing are more open to the campaign, while the effect on the total sample is not statistically significant. Furthermore, the intervention increases the overall perception that corruption is a (long-term) part of society rather than a temporary phenomenon. Finally, students with experience in corrupt practices tend to adopt a more negative view of corruption. For those without such experiences, however, we find some indication that the treatment could bolster the acceptance of corruption by instructing the students about its dissemination. The effects of this intervention are therefore ambivalent and appear to depend on the students’ previous exposure to corruption

On the development of students’ attitudes towards corruption and cheating in Russian universities

Based on empirical data from selected public universities in Khabarovsk, Russia, this paper compares first and fifth year students regarding their attitudes towards corruption in general and university corruption in particular. Even after making both groups of students comparable with respect to a range of socio-economic characteristics by a matching approach, the results suggest that fifth year students are more open to a range of informal and corrupt practices than first years. Our analysis therefore points to the possibility that the Russian higher education system might ‘favor’ compliance with corruption and informal practices, with potentially detrimental consequences for the Russian society as a whole