About a book on integral calculus I am currently a second year undergraduate student in mathematics; I am taking Integral Calculus, however I have run into a difficulty.
This is the discomfort that some books of integral calculus generate in me, for the moment I am using Spivak's book of infinitesimal calculus, however I want to know which books you recommend me to strengthen my learning of integral calculus. This taking into account that the book should be focused on mathematicians.
Thanks
 A: So this is my view on calculus books. The best book on calculus is Fichtenholz, Differential und Integralrechnung. It is 3volumes. The original is russian, and it has been translated into german and polish.  It is solid and rigorous exposition of all issues in calculus with many examples.
Another classic book is Joseph Edwards, Treatise on Integral Calculus 2vols. It is in english and can be found online on internet archive. It is very extensive on examples and methods of integration, but it does not cover theoretical aspects.
He also has Integral Calculus for Beginners, a smaller and more approachable book. And has books on Differential calculus.
Another traditional text is Todhunter, Treatise on Integral Calculus, and Treatise on Differential Calculus, less extensive than Edwards, but easier to assimilate.
The modern text for rigorous calulus is Rudin, Principles or Real Analysis. Solid proofs of the theory, although using topological concepts, but weak on examples.
Another good book is Philip Franklin, Treatise on Advanced Calculus.
Looking at your example, it is more of a practical question and not so much theoretical, I recommend Todhunter, or Edwards, Integral Calculus for Beginners whichever you find better.
Of course, this list betrays my preference for older books.
Finally, one cannot become an expert in any subject by reading one book no matter how good it is, you must read several.
