A. Blouza et H. Ledret, ON THE INFINITESIMAL RIGID DISPLACEMENT LEMMA, Comptes rendus de l'Academie des sciences. Serie 1, Mathematique, 319(9), 1994, pp. 1015-1020
We give a new proof of the infinitesimal rigid displacement lemma for
a shell, under hypotheses of regularity for the displacement and the m
idsurface of the shell that are weaker than those required by earlier
proofs.