We present a model independent method of reconstructing the Lagrangian for the k-essence field driving the present acceleration of the universe. We consider the simplest k-essence model for which the potential is constant. Later we use three parametrizations for the Hubble parameter H(z), consistent with recent the SN1a data, to yield the Lagrangian F . Our reconstruction program does not gener...

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We show that several constraint propagation algorithms (also called (local) consistency, consistency enforcing, Waltz, filtering or narrowing algorithms) are instances of algorithms that deal with chaotic iteration. To this end we propose a simple abstract framework that allows us to classify and compare these algorithms and to establish in a uniform way their basic properties. Note. This is a ...

In this paper, we give a re-formulation of our previously defined distillation algorithm, which can automatically transform higherorder functional programs into equivalent tail-recursive programs. Our re-formulation simplifies the presentation of the transformation and hopefully makes it easier to understand. Using distillation, it is possible to produce superlinear improvement in the run-time ...

“I’m late, I’m late ...” cries the Mad Hatter in Alice in Wonderland. Mad though he may be, he seems to be singing our song. How often do conversations end abruptly when one conversant looks at his watch and leans impatiently into the “rush” position? How often do people dash past each other, eyes averted, muttering “Late for a meeting, gotta run...” as a substitute for a personal greeting and ...

Development of languages for specifying or modelling problems is an important direction in constraint modelling. To provide greater abstraction and modelling convenience, these languages are becoming more syntactically rich, leading to a variety of questions about their expressive power. In this paper, we consider the expressiveness of Essence, a specification language with a rich variety of sy...

Empowering learners and using powerful techniques are prominent elements in the discourse of adult and vocational education. But what constitutes the elements of what might be considered as powerful teaching? This paper begins by examining the way educators talk about power and then proposes four elements that lie at the heart of powerful teaching; understanding how power dynamics intersect wit...

Abstraction is the cornerstone of high-level programming; HTML forms are the principal medium of web interaction. However, most web programming environments do not support abstraction of form components, leading to a lack of compositionality. Using a semantics based on idioms, we show how to support compositional form construction and give a convenient syntax.