GENERAL RELATIVITY AND GRAVITATION, cilt.31, sa.3, ss.391-403, 1999 (SCI-Expanded)
We show spurious effects in perturbativecalculations due to different orderings of inhomogeneousterms while computing corrections to Green functions fortwo different metrics. These effects are not carried over to physically measurable quantities likethe renormalized value of the vacuum expectation valueof the stress-energy tensor.