Logic with Trees: An Introduction to Symbolic Logic

I studied this book as college-level introductary logic course textbook. The book is not hard to understand except for the last two chapters, which try to deal with somehow advanced topics, but not very clearly. But the rest of the book is nicely written overall(although it has a few mistypings) And I want to point out that this textbook is basically not written in mathematics style. It doesn't contain many equations and theorems as in mathematics textbooks, instead it explains things in written English.