Hamiltonian approach to lagrangian gauge symmetries

We reconsider the problem of finding all local symmetries of a Lagrangian. Out approach is completely Hamiltonian without any reference to the associa ted action. We show that the restrictions on the gauge parameters entering in the definition of the generator of gauge transformations follow from the commutativity of a general gauge variation with the time derivative operat ion. (C) 1999 Elsevier Science B.V. All rights reserved.