On some types of exact solutions of the Einstein equation. 2

Several types of the Einstein spaces which can describe gravitational waves are investigated. When the solutions of the Einstein equations are found, additional conditions are imposed on the metrics under consideration. It is required: 1) that the spaces should admit the two-parametric Abelian group of motion; 2) that the wave coordinate system would be privileged; 3) that bicharacteristics of the Einstein equation would satisfy the harmonicity condition. The superposition of the enumerated conditions has made it possible to perform a complete integration of the Einstein equations. The solutions obtained are interpreted as the wave ones