The Absence of Killing Fields is Necessary for Linearization Stability of Einstein's Equations Judith ArmsJerrold Marsden Indiana University Mathematics Journal 1979 text pdf 10.1512/iumj.1979.28.28008 10.1512/iumj.1979.28.28008 en Indiana Univ. Math. J. 28 (1979) 119 - 125 state-of-the-art mathematics http://iumj.org/access/