Undergraduate philosophers at Cambridge take several courses in formal logic. As far as possible, I think it is best to teach these courses with Open Education Resources. We currently use the following:
The links will take you to a page describing the book, and allowing you to download it (in various formats). All three books are released under Creative Commons BY 4.0 licences. So you can download, share, and remix them, free of charge (subject to minor constraints).
Last modified 21 Jan 2019