Gravitation. What is this?

The concept of an "inertial frame" (its existence is assured by the Newton First Law) will be analyzed in detail. Gravitational field can be understood as a field of local inertial frames. From this point of view, the (pseudo) metric tensor describes only a small sector of the complete theory, including also electromagnetism and yet another kind of matter. Mathematically, such a complete theory can be understood as the correct implementation of the old ideas due to Einstein, Weyl, and Born-Infeld.