Our very own Katie Steckles is currently residing mathematically in the University of Greenwich’s Stephen Lawrence Gallery. She’s there until Tuesday the 26th, doing a variety of numerical, geometrical and otherwisely logical things for anyone who pops along.

# You're reading: Posts By Christian Perfect

### Integral House is for sale!

You might have heard the story about the author of a calculus textbook that made so much money he could afford to build a mansion in the shape of an integral symbol.

Well, his name was James Stewart and he died last December, so now Integral House is up for sale, for $23m.

Yes, textbooks are *that* ridiculously expensive in North America.

The Daily Beast has written an article about the sale, and there’s a good thread on MetaFilter with a mix of discussion about the house itself and lots of griping about the American textbook racket.

### The Open Logic Project – an open-source, collaborative logic textbook

Good news, logic fans! The *Open Logic Project* is a project to write an open-source textbook on logic. And if you read it, you’ll find tautologies like the last sentence completely thrilling.

The book is aimed at a non-mathematical audience, mainly computer science and philosophy students, so it assumes very little knowledge of the basics. The project was instigated by Richard Zach, who’s Professor of Philosophy at the University of Calgary. The rest of the project team consists of Aldo Antonelli, Andy Arana, Jeremy Avigad, Gillian Russell, Nicole Wyatt, Audrey Yap, and Richard Zach. They’re aiming to cover first-order logic, sequent calculus, soundness and completeness theorems, computability theory, and incompleteness. If things go well, they want to add material about model theory, computability and Turing machines (that’s already in progress), and some stuff on philosophy of language and mathematics.

A high-quality textbook for free would be pretty good on its own, but what’s really nifty is that the source code has been set up so the book is configurable to your tastes: you can say what kind of notation you’d like, and even adapt theorems and lemmas to use different proof systems.

### More information

The Open Logic Project official website

Get the source code and contribute on GitHub

@OpenLogicProj on Twitter

### The Journal of K-Theory is dead

Following on from the resignation of the editorial board, CUP has announced that it’s not publishing the Journal of K-Theory any more. The new journal started by the former editors, *Annals of K-Theory*, aims to start publishing papers online this year.

### Review: CALX, a calculator for iPhone

Reader Danial Clelland wrote in to tell us about his new calculator app for iPhone, CALX.

None of us owns an iPhone, but I borrowed someone else’s for a while and had a brief look at the app.

### The Aperiodical is 3

The Aperiodical turned three on Saturday. I was away attending my brother’s wedding, but I couldn’t let the birthday pass without mention.

In three years we’ve published 1,462 posts (make that 1,463 including this one) by 32 authors, read by 713,000 visitors.

Thanks for reading!

### #thatlogicproblem round-up

C:$K_A m; \\ K_B d.$

A:$\neg K_A d; \\ m \vDash \neg K_B m.$

B:$d \not\vDash K_B m; \\ (K_A(\neg K_B m)) \vDash K_B (m,d).$

A:$m \wedge K_B(m,d) \vDash K_A (m,d).$

Albert, Bernard and Cheryl have had a busy week. They’re the stars of #thatlogicproblem, a question from a Singapore maths test that was posted to Facebook by a TV presenter and quickly sent the internet deduction-crazy.

First of all: no, it’s not meant to be answered by an average Singaporean student. It’s a hard question from a schools Olympiad test.