Einstein used a complicated set of tensors in his General Relativity.

However in his writing in 1916 he used a Laplace operator, which can help us to determine the gravitational potential inside a sphere without having to go into his field equations.

Many surprising results: The behaviour of clocks is in line with all experiments and now we have a repaired Schwarzschild solution.

Revolutionary against many publications: No eventhorizon outside a sphere exists, because the Schwarzschild radius is always smaller than the sphere radius!