"Differential geometry." . . "Calculus of variations." . . . . . "On the vanishing of the curl of a certain velocity field occurring in the theory of conservative holonomic dynamical systems"@en . . . . . . . . . . . . "Vector analysis." . . "Integrals." . . "Topology." . . "Differential equations." . . "Dynamics." . . . . "THOMPSON RAMO WOOLDRIDGE INC LOS ANGELES CALIF." . . "Set theory." . . "Invariance." . . "Velocity." . .