This truly outstanding book explains proofs, theory and structure of some of the most core areas of mathematics, and does so in a way that is clear, comprehensible and compelling.  To do so in areas as complex and as abstract as these subjects are is no mean feat, but Dr. Warner makes it look easy.  It is the best book I could have obtained as I am contemplating pursuing a Masters in math after receiving my bachelors degree over fifty years ago.  This text provides me with a perfect vehicle for review and update.  I rate it six stars out of a possible five!