On the variational derivation of Einstein's strong field equations

L. J. Gregory, A. H. Klotz
1976 The Journal of the Australian Mathematical Society Series B Applied Mathematics  
It is shown that the necessary and sufficient condition for the transposition invariance of the field equations derivable from an Einstein-Kaufman vanational action principle is the vanishing of the vector P A . When this condition is satisfied, the field equations become the so-called strong field equations of Einstein. In this sense, the latter can be claimed to follow from the same action principle.
doi:10.1017/s0334270000001235 fatcat:w5xxhqyjb5gajnkefqqenijkpa