Q1. What are the contributions mentioned in the paper "On the algebraic invariants of the four-dimensional riemann tensor" ?
Recently, Sneddon ( 1986 ) discussed briefly the form in which several authors have presented the fourteen independent algebraic invariants ( Haskins 1902 ) $ of the Riemann curvature tensor in four dimensions. Among the authors mentioned were GChCniau and Debever ( 1956a, b, c ) with implied priority of publication. The fourteen scalars according to Narlikar and Karmarkar are constructed from the following tensors. In this paper is determined the number of algebraic invariants as a function of the dimension of the space.