Probability Theory: A Concise Course (Dover Books on Mathematics) - GOOD

Number Theory (Dover Books on Mathematics)

A Book of Set Theory (Dover Books on Mathematics)

Dover Books on Mathematics Ser.: Proof Theory by Gaisi Takeuti (2013, Paperback)

Introductory Graph Theory (Dover Books on Mathematics) - Paperback - VERY GOOD

Group Theory (Dover Books on Mathematics) - W. R. Scott

A Course on Group Theory (Dover Books - Paperback, by John S. Rose - Very Good

Probability Theory: A Concise Course (Dover Books on Mathematics)