Two-dimensional metric and tetrad gravities as constrained second order   systems
  Using the Gitman-Lyakhovich-Tyutin generalization of the Ostrogradsky method for analyzing singular systems, we consider the Hamiltonian formulation of metric and tetrad gravities in two-dimensional Riemannian spacetime treating them as constrained higher-derivative theories. The algebraic structure of the Poisson brackets of the constraints and the corresponding gauge transformations are investigated in both cases. 
R. N. Ghalati, N. Kiriushcheva and S. V. Kuzmin