Hofstra University: Stefan Waner and Steven R. Costenoble's "Introduction to Logic"
Read this page. This text will enable you to see the very close connection between propositional logic and naïve set theory, which you will study in Unit 3.
Click http://web.archive.org/web/20111127043555/http:/people.hofstra.edu/stefan_waner/Realworld/logic/logic1.html link to open resource.