The monograph of the master G. S. Friedstein, known for his work in the field of debut theory, is dedicated to one of the most relevant chess principles, which is part of the repertoire of the world's strongest grandmasters. It summarizes and systematizes rich practical and theoretical material, takes into account the latest research of Soviet and foreign chess players in the defense of Pirts-Ufimtsev. The book contains explanatory parts with comments by the author.