Teach Yourself Logic: A Study Guide [pdf]
I'd like to recommend Logic 2010[1], a application with which you can do logic exercises to learn the natural deduction system from *"Logic: Techniques of Formal Reasoning" by Kalish, Montague, and Mar.[2]<p>The program is officially only for MacOS and Windows, but with a little work it's possible to get it running on Linux, as it's just Java.<p>The exercises are fun, and the program will not only check your work to make sure it's right, but also point out where and sometimes why it's wrong.<p>[1] - <a href="https://logiclx.humnet.ucla.edu/Logic/Download" rel="nofollow">https://logiclx.humnet.ucla.edu/Logic/Download</a><p>[2] - <a href="https://www.amazon.com/Logic-Techniques-Reasoning-Donald-Kalish/dp/0195155041" rel="nofollow">https://www.amazon.com/Logic-Techniques-Reasoning-Donald-Kal...</a>