Question on the Existence of Gravitational Anomalies

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The existence of gravitational anomalies claimed by Alvarez-Gaume and Witten is examined critically. It is pointed out that they were unaware of the essential difference between T-product quantities and T*-product quantities. Field equations and, therefore, the Noether theorem are, in general, violated in the case of T*-product quantities, that is, those directly calculable from Feynman integrals. In the 2-dimensional case, it is explicitly confirmed that the energy-momentum tensor is strictly conserved if the above stated property of the T*-product quantities is correctly taken into account. The non-existence of gravitational anomalies is explicitly demonstrated for the BRS-formulated 2-dimensional quantum gravity in the Heisenberg picture.