We’ve kept this on the down-low long enough, I think: together with Aldo Antonelli, Jeremy Avigad, Nicole Wyatt, and Audrey Yap, I’ve been working on an open source advanced logic textbook for a little while; Andy Arana and Gillian Russell are also on the editorial board. It’s far from done; in fact the whole idea is that it will never be done. But, as they say, release early, release often.

We’re thinking of it as aimed at an audience of advanced undergraduate/graduate philosophy students. Nicole has been teaching Calgary’s Logic II from it, and I’ve used it to teach Intermediate Logic at McGill last term. It currently covers naive set theory, soundness and completeness of first order logic, recursive functions, and incompleteness.  Some of it was written specifically for the text, other parts are based on existing lecture notes (esp., Aldo’s notes on model theory and Jeremy’s on computability and incompleteness).  As time goes on, we’ll include material on Turing machines (planned for the coming fall semester), model theory, modal logic, and other topics of interest. We take requests, and we welcome contributions.

There’s a website, for more info: openlogicproject.org

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(This is not the only free/online logic textbook project, but one of perhaps only two that are open.  See this list.)