Einstein Geometrization Philosophy and Differential Identities in   PAP-Geometry
  The importance of Einstein's geometrization philosophy, as an alternative to the least action principle, in constructing general relativity (GR), is illuminated. The role of differential identities in this philosophy is clarified. The use of Bianchi identity to write the field equations of GR is shown. Another similar identity in the absolute parallelism geometry is given. A more general differential identity in the parameterized absolute parallelism geometry is derived. Comparison and interrelationships between the above mentioned identities and their role in constructing field theories are discussed. 
M. I. Wanas, Nabil L. Youssef, W. El Hanafy and S. N. Osman
gr-qc math.DG