Compatibilite des Equations de la Theorie Unitaire du Champ d'Einstein Andre Lichnerowicz Indiana University Mathematics Journal 1954 text pdf 10.1512/iumj.1954.3.53025 10.1512/iumj.1954.3.53025 en Indiana Univ. Math. J. 3 (1954) 487 - 521 state-of-the-art mathematics http://iumj.org/access/