Leandro Conde

One of the best treatises on Differential Geometry I've read, personally, and don't get fooled by the "Elementary" in the title... it's pretty thorough and deep reaching.

A great book introducing a far superior notational system for hyper-numbers in general, that for some reason I have hardly ever seen referenced. Perhaps it's because it's supposed to be a Mathematical book which takes the approach of applying the idea of using indexes to define quantities that mathematicians often see formally as maps, or, forms... where the index notation is something left for physicist-only. But in this case the index notation is just a formal device with formal rules that has nothing to do with the normal use of notation in physics-only treatises and the notation is so much better that is hard to see a reason for it to be mostly ignored, it seems. And the notation is so much better for actual calculations too. I'd recommend a read to anyone that's knowledgeable in tensor, or at least, vector calculus, and want to see a different approach to the standard notation used in the normal treatises... and then see it be generalized it to cover so much more too!