Trying again to fail-first

For constraint satisfaction problems (CSPs), Haralick and Elliott [1] introduced the Fail-First Principle and defined in it terms of minimizing branch depth. By devising a range of variable ordering heuristics, each in turn trying harder to fail first, Smith and Grant [2] showed that adherence to this strategy does not guarantee reduction in search effort. The present work builds on Smith and Grant. It benefits from the development of a new framework for characterizing heuristic performance that defines two policies, one concerned with enhancing the likelihood of correctly extending a partial solution, the other with minimizing the effort to prove insolubility. The Fail-First Principle can be restated as calling for adherence to the second, fail-first policy, while discounting the other, promise policy. Our work corrects some deficiencies in the work of Smith and Grant, and goes on to confirm their finding that the Fail-First Principle, as originally defined, is insufficient. We then show that adherence to the fail-first policy must be measured in terms of size of insoluble subtrees, not branch depth. We also show that for soluble problems, both policies must be considered in evaluating heuristic performance. Hence, even in its proper form the Fail-First Principle is insufficient. We also show that the “FF” series of heuristics devised by Smith and Grant is a powerful tool for evaluating heuristic performance, including the subtle relations between heuristic features and adherence to a policy

Left Recursion in Parsing Expression Grammars

Parsing Expression Grammars (PEGs) are a formalism that can describe all deterministic context-free languages through a set of rules that specify a top-down parser for some language. PEGs are easy to use, and there are efficient implementations of PEG libraries in several programming languages. A frequently missed feature of PEGs is left recursion, which is commonly used in Context-Free Grammars (CFGs) to encode left-associative operations. We present a simple conservative extension to the semantics of PEGs that gives useful meaning to direct and indirect left-recursive rules, and show that our extensions make it easy to express left-recursive idioms from CFGs in PEGs, with similar results. We prove the conservativeness of these extensions, and also prove that they work with any left-recursive PEG. PEGs can also be compiled to programs in a low-level parsing machine. We present an extension to the semantics of the operations of this parsing machine that let it interpret left-recursive PEGs, and prove that this extension is correct with regards to our semantics for left-recursive PEGs.Comment: Extended version of the paper "Left Recursion in Parsing Expression Grammars", that was published on 2012 Brazilian Symposium on Programming Language

The End of Mystery

Tim travels back in time and tries to kill his grandfather before his father was born. Tim fails. But why? Lewis's response was to cite "coincidences": Tim is the unlucky subject of gun jammings, banana peels, sudden changes of heart, and so on. A number of challenges have been raised against Lewis's response. The latest of these focuses on explanation. This paper diagnoses the source of this new disgruntlement and offers an alternative explanation for Tim's failure, one that Lewis would not have liked. The explanation is an obvious one but controversial, so it is defended against all the objections that can be mustered

A Comedy of Errors or, How I Learned to Stop Worrying and Love Sensibility‐Invariantism about ‘Funny’

In this article, I argue that sensibility‐invariantism about ‘funny’ is defensible, not just as a descriptive hypothesis, but, as a normative position as well. What I aim to do is to make the realist commitments of the sensibility‐invariantist out to be much more tenable than one might initially think them to be. I do so by addressing the two major sources of discontent with sensibility‐invariantism: the observation that discourse about comedy exhibits significant divergence in judgment, and the fact that disagreements about comedy, unlike disagreements about, say, geography, often strike us as fundamentally intractable

You Will Respect My Authoritah!? A Reply to Botting

In a paper and a reply to critics published in _Informal Logic_, I argue that arguments from expert opinion are weak arguments. To appeal to expert opinion is to take an expert’s judgment that _p_ is the case as evidence for _p_. Such appeals to expert opinion are weak, I argue, because the fact that an expert judges that _p_ does not make it significantly more likely that _p_ is true or probable, as evidence from empirical studies on expert performance suggests. Unlike other critics of this argument, who take issue with the empirical evidence on expert performance, David Botting says that he wants to take issue with the premise that reliability is a necessary condition for the strength of appeals to expert opinion. I respond to Botting’s objections and argue that they miss their intended target. I also argue that his attempt to show that arguments from expert opinion are strong is unsuccessful

X.509 certificate error testing

X.509 Certificates are used by a wide range of technologies to verify identities, while the SSL protocol is used to provide a secure encrypted tunnel through which data can be sent over a public network. Combined both of these technologies provides the basis of the public key infrastructure (PKI). While the concept of PKI is a good idea, the different implementation of the technologies in different operating system and clients often lead to weaknesses. This paper proposes a methodology to automate the testing of SSL clients by generating both bogus and malformed certificates in order to evaluate the client’s response and identify potential threats to network infrastructures

Emily Dickinson in vain

This is a biography of the nineteenth century poet, Emily Dickinson.Women's and Gender Studie

Refugee Resettlement and Integration in Germany: Analysis of Media Discourse

Refugees are among the most discussed and debated topics worldwide; the massive movement of refugees and asylum seekers facing the world today is the largest since the end of the second world war. The United Nations High Commissioner for Refugees (UNHCR) estimates the total number of refugees in the world to be almost twenty-six million people, while asylum seekers account for around three million. The concept of a refugee is formally defined by the 1951 Convention on the Status of Refugees, which creates a legal status, and states that a refugee is a person who “faces well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion”. The issues surrounding refugees are vast and complex, with wide-reaching and long lasting effects. As the world continues to face massive human displacement as a result of fragile states, civil wars, and countless other factors, refugees and related issues will continue to be of vital importance. One key element to the issue of refugees is the question of resettlement and even further the issue of integration

Forgetting

Forgetting is importantly related to remembering, evidence possession, epistemic virtue, personal identity, and a host of highly-researched memory conditions. In this paper I examine the nature of forgetting. I canvass the viable options for forgetting’s ontological category, type of content, characteristic relation to content, and scale. I distinguish several theories of forgetting in the philosophy and psychology of memory literatures, theories that diverge on these options. The best theories from the literature, I claim, fail two critical tests that I develop (the metacognition and prospection tests), underwriting arguments against the theories. I introduce a new theory about the state of forgetting—the learning, access failure, dispositional (LEAD) theory: to forget is to fail to access something that is both learned and either inaccessible or intended to be accessed. I argue that the LEAD theory of forgetting is the lead theory of forgetting. It passes the metacognition and prospection tests, and has several further virtues at no cost. Finally, I advocate reductionism about the process of forgetting; the process reduces wholly to states of forgetting. In particular, a process of forgetting is just a sequence of increasingly strong states of forgetting