GUILLE,
no idea why your access to this site is denied. Maybe this site only accessable from the U.S. and that it's related to other sites funded by the U. S. federal government.
But about the principle of equivalence, the following book by S. Weinberg gave an extensive discussion.
Weinberg, S.
Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity. New York: Wiley, 1972.
Linear Mode
