Hello all, I am about to go into vector analysis (next week) and I just wanted to knock out a few books on the subject of integration mainly. I have read through my vector calculus book (P.C. Matthews) and there were a few things that threw me off, but made complete sense when I thought about them. I.e. Why is it okay to split a double (or triple) integral up into a product? ∫∫∫(xyz)dxdydz = (∫xdx)(∫ydy)(∫zdz) I never saw this explained in any book explicitly, but some books (as well as professors) do it, and I am just wondering why this, and the opposite of this, is true; I am not comfortable using rules that I do not fully understand, but sometimes I have to do things like this. I think my main problem is I learned how to do integration one way, and I am stuck in that way, but I see that it is limiting me in my ability to recognize things. I am very comfortable with integration, and with calculus in general, but I feel as though there are some gaps in my fundamental understanding of integration. I would just like some book/resource recommendations to try to fill these gaps. I have not taken DE yet, so I do not know if that class will have the answers I am looking for. Anyways, thank you all in advance for your replies.