While I have a ton of favorite math books, the two books that I felt really helped me the relevant subject are: * An Introduction to Manifolds by Loring Tu *

While I have a ton of favorite math books, the two books that I felt really helped me the relevant subject are: * An Introduction to Manifolds by Loring Tu * The Elements of Integration and Lebesgue Measure by Robert G. Bartle. These two books were instrumental to my studying for my qualifying exams.