After 15 years of effort to grow this apple tree, it has finally dropped its first fruit, namely our volume “Einstein’s Apple” which is now available in hardcover and e-book formats from World Scientific via
http://www.worldscientific.com/worldscibooks/10.1142/9333
The work provides an accessible introduction to concepts such as teleparallelism and torsion that are slighted in many courses; historical introduction sections include the early uses of these concepts and Einstein’s own early insights.
Cheers, Eugene Surowitz