A RUDN University mathematician has proposed a new criterion for solving the Boussinesq equations. These equations describe the nonlinear propagation of waves in certain media, e.g. plasma, a surface of liquid of shallow depth, and so on. They examined the Boussinesq equation in three-dimensional space and derived a criterion for uniqueness and the existence of important solutions of a special type to the Boussinesq partial differential equation. The proposed criterion has applications in mechanics of continuous media, which studies the motion of liquids and gases. The article was published in Bulletin of the Brazilian Mathematical Society, New Series.