I am interesting in teaching myself General Relativity, since I only learned Special Relativity during my bachelor in Physics. Now, I have turned into math, but nevertheless I remember enjoying theoretical physics and in particular relativity, I know that G.R. is a beautiful mathematical construction. I know the basis of Differential Geometry (Riemannian, Pseudo-Riemannian, Banach manifolds and Lie groups). I ordered General Relativity by Robert M. Wand. But honestly, I found the notation to be very cumbersome.
I know physicists find it more useful to deal with tensors in general in terms of a coordinate system, but I myself feel more comfortable with the abstract definition knowing a priori how such tensor should transform (from chart to chart). Also, Einstein summation convention does not do too much for me, I often forget whether or not I was summing. So, is there a good book you could recommend me to learn the general theory of relativity? I am more interested in the foundations and fundamental principles than in the applied stuff (Black holes, gravitational lenses, etc.).