## Recent News

#### 28 February 2015

I have known about the Mathematical Genealogy Project for quite some time, but, prompted by Richard Zach I notice two new and wonderful things.

First, David Alber has produced in Geneagrapher a neat tool to download genealogy data and save a .dot file, which can be read by Graphviz and displayed as a directed graph.

Here’s a detail from my genealogy. (This image is a link to a pdf file of the entire thing.)

### Classes in Semester One

#### 25 February 2015

Teaching started for first semester, with the launch of Logic: Language and Information 1 on Coursera. That’s been a lot of fun already, with over 17,000 enrolled. There’s something very exciting about being involved with a large number of students all around the world, choosing to work hard to learn logic for the first time.

### Ash Wednesday

#### 18 February 2015

Rembember that you are dust, and to dust you shall return.

Remember that you are dust (@consequently) on

### Do LNC and LEM suffice to define negation?

#### 17 February 2015

What is negation?

One answer you find in the literature is that negation is the operator that makes each instance of the Law of the Excluded Middle (LEM) and the Law of Non-Contradiction (LNC) turn out to be true. That is, every sentence of the form $p\lor \neg p \qquad \neg(p\land\neg p)$ is true, no matter what sentence we use in the place of $$p$$ (where $$\neg$$ stands for negation, $$\lor$$ for disjunction, and $$\land$$ for conjunction).

This is the wrong way to try to define negation. If you read on, I’ll explain why.

#### 13 February 2015

I’ve added a search feature to the site in the footer of each page. There seems to be enough on the site that search is genuinely useful.

I’ve used DuckDuckGo, which has a comprehensive index of this place, and which can be styled to match the visual treatment of the rest of the site. Please let me know if there are any problems with the implementation.

## Recent Writing

• “Assertion, Denial, Accepting, Rejecting, Symmetry and Paradox,” to appear in Foundations of Logical Consequence, edited by Colin R. Caret and Ole T. Hjortland, Oxford University Press, 2015 Abstract  pdf
• “Normal Proofs, Cut Free Derivations and Structural Rules,” Studia Logica 102:6 (2014) 1143–1166. Abstract  pdf
• “Pluralism and Proofs,” Erkenntnis 79:2 (2014) 279–291. Abstract  pdf
• “Assertion, Denial and Non-Classical Theories,” pp. 81–99 in Paraconsistency: Logic and Applications, edited by Koji Tanaka, Francesco Berto, Edwin Mares and Francesco Paoli, 2013. Abstract  pdf
• Special Issue of the Logic Journal of the IGPL on Non-Classical Mathematics, Volume 21, issue 1, 2013. Abstract  pdf