  We show that Einstein equations are compatible with the presence of massive
point particle idealization and find the corresponding two parameter family of
solutions. They are complete defined by the bare mechanical mass $M>0$ and the
Keplerian mass $m>0$ ($m < M$) of the point source of gravity. The global
analytical properties of these solutions in the complex plane define a unique
preferable radial variable of the one particle problem.
  These new solutions are fundamental solutions of the quasi-linear Einstein
equations. We introduce and discuss a novel nonlinear superposition principle
for solutions of Einstein equations and discover the basic role of the
relativistic analog of the Newton gravitational potential. For the relativistic
potential we introduce a simple quasi-linear superposition principle as a new
physical requirement for the initial conditions for Einstein equations, thus
justifying the instant gravistatic case for N particle system.
  This superposition principle allows us to sketch a new theory of the
gravitational mass defect. In it a specific Mach-like principle for the
Keplerian mass $m$ is valid, i.e. it depends on the mass distribution in the
universe, in contrast to the bare mass $M$, which remains a true constant.
Several basic examples both of discrete and of continuous mass distributions
are considered.
