A CRITERION OF THE EXISTENCE OF GENERALIZED INTEGRAL VARIATIONAL-PRINCIPLES FOR GIVEN EQUATIONS Статья SAVCHIN V.M. Differential Equations. Том 29. 1993. С. 1235-1241
ON THE STRUCTURE OF VARIATIONAL EQUATIONS WITH THE SYMMETRICAL OPERATOR D DT Статья SAVCHIN V.M. Differential Equations. Том 29. 1993. С. 1532-1537