A Logical Introduction to Proof

From the reviews:

“Cunningham (Buffalo State, SUNY) focuses on the strategies for different proof techniques. ... The well-written text is consistent in its focus, which should help students. The book includes sufficient, appropriate exercises. ... contains ample notes to guide students through most of the exercises. Whether used for a course or as a reference for students learning proof techniques, this book is certainly worthy of consideration. Summing Up: Highly recommended. Lower-division undergraduates through graduate students.” (J. R. Burke, Choice, Vol. 51 (1), September, 2013)