“…-The solutions of the equations (1) determine a family of contact transformations, see [30,11,21,28]; -The generalized variational principle gives a variational description of energynonconservative processes even when F in (1) is independent of t. -If F has the form F = −λ u + L(x, v), then the relevant problems are closely connected to the Hamilton-Jacobi equations with discount factors (see, for instance, [19,18,9,34,35,37,29,36]). As an extension to nonlinear discounted problems, various examples are discussed in [14,43]. -Even for a energy-nonconservative process which can be described with the generalized variational principle, one can systematically derive conserved quantities as Noether's theorems such as [26,27]; -The generalized variational principle provides a link between the mathematical structure of control and optimal control theories and contact transformation (see [25]); -There are some interesting connections between contact transformations and equilibrium thermodynamics (see, for instance, [39]).…”