Equation with Two Variables

The story

While selling goods in the train carriage, Mkhitar notices his peer, Karen, who has his feet on the front seat and his head hanging on the textbook. Silently obeying Mkhitar's remark, Karen lowers his legs and turns his back. Mkhitar, tries various methods to contact the stranger. Karen, with the bag hanging around his neck, shouts in the train carriages and tries to sell Mkhitar's goods, while Mkhitar is deep in his thoughts: is he thinking about the chess problem or life in general?