Hi, I started reading General Relativity but concepts such as Lorentz transformations, rotations, tensors etc. are, at least in my opinion, poorly explained. Or perhaps the authors assume that the readers are already familiar with such maths? At any rate, I would very much like to read some good books on the above math topics. Could anyone recommend me some books / textbooks? I really need to understand it well, from the basics to the very difficult concepts. The more detailed, the better (and preferably with exercises and solutions, if possible, so that I can also practice the maths (and check my solutions), not just read the book). Just a few words on difficulty. It seems to me that there are two meanings for "difficult". One of them is "too much detail". I don't mind that kind of "difficult". So yes, please do tell me about "the epsilon and the delta" of Ricci calculus etc. On the other hand, if "difficult" means that the book takes you through the whole history of mathematics before actually introducing the concept, then I am afraid that's not what I am looking for. Although if the latter are the only kind of books you would recommend, then they are obviously better than nothing. So the short of it is: I am not afraid of difficult, and in fact I really want to understand the topic THOROUGHLY, but I don't want to waste my time with unnecessary details either.