Peter Smith (Cambridge) is generously providing tremendous resources for students, whether beginning or advanced, setting out to study logic. In a recent email, he writes:
Students are having a rotten time right now. It’s good to do what we can to make learning materials more easily available (a pretty small thing, but something). So: I’ve now made corrected versions of the second editions of
Peter Smith, An Introduction to Formal Logic
Peter Smith, An Introduction to Gödel’s Theorem
(originally published by CUP) both available as free PDF downloads (for anyone who wants a hard copy, there are also at-cost Amazon print-on-demand reprints).
The first is an introduction originally based on the Cambridge first year course for philosophers. The second, although published in a philosophy series too, could be of more interest to mathematicians as it is more maths than philosophical commentary.
More information and links at my website, https://www.logicmatters.net
Please spread the word to anyone you think might be interested.