Solution of Constraints in Theory of Relativistic String
  The Hamiltonian theory of a relativistic string is considered in a specific reference frame in terms the diffeo-invariant variables. The evolution parameter and energy invariant with respect to the time-coordinate transformations are constructed, so that the dimension of the kinemetric group of diffeomorphisms coincides with the dimension of a set of variables whose velocities are removed by the Gauss-type constraints in accordance with the second Noether theorem. This coincidence allows us to solve the energy constraint, and fulfil Dirac's Hamiltonian reduction. 
B.M. Barbashov and V.N. Pervushin