Comments on the article ‘M.O. Katanaev, Complete separation of variables in the geodesic Hamilton-Jacobi equation in four dimensions, Physica Scripta (2023), 98, 104001’

The present note is a feedback on the article by M.O. Katanaev in Physica Scripta (2023, 98, 104 001) , where, in our opinion, a distorted view of the classical theory of separation of variables in the Hamilton-Jacobi equation is given. We show that the metrics given in this paper, addmiting separation of variables, are special cases of V.N. Shapovalov metrics (Siberian Mathematical Journal, 1979, 20, 790) , finally obtained in the 70s of the last century. The results of the article in question, unlike the original ones, do not have scientific novelty and contain omissions and incorrect statements.