Problem B1 (40 pts). Give a context-free grammar for the language over the alphabet {a, b, c} given by L = {xcy | x 6= y, x, y ∈ {a, b}∗}. Hint . At first glance, this seems impossible. Think nondeterministically. You need to figure out how to express that x 6= y in such a way that you can write grammar rules that enforce this condition. Obviously, this is the case if |x| < |y| or |y| < |x|. An...

The bicentenary of the publication of William Withering's Foxglove has been well and largely perceptively celebrated the world over, but the most permanent tribute comes in the form ofthis book by J. K. Aronson. Aronson is very well qualified for the job he has set himself. He is an eminent authority on the pharmacology and clinical practice involved, and he now shows himself to be a fine and m...

In this chapter, we present a complementary pair of experiments on the way users edit Wikipedia. First, we look at the macro scale, quantitatively categorising the types of edits users made. Then, we look at the micro scale, qualitatively studying the rationale and process of individual editors. These experiments form part of a broader project looking into the potentially beneficial relationshi...

Most people have experienced distressing events that they would rather forget. Although memories of such events become less intrusive with time for the majority of people, those with posttraumatic stress disorder (PTSD) are afflicted by vivid, recurrent memories of their trauma. Often triggered by reminders in the daily environment, these memories can cause severe distress and impairment. We pr...

O ver the years I have gotten into trouble more than a few times for things I have written or said in public, but I suppose the chief cause of my notoriety is a speech I gave to the freshmen of Yale College suggesting that they would be wise to make the study of Western civilization the center of their pursuit of a liberal education. In that speech I focused on our needs as Americans. I pointed...