N. Qian, TANGENTIAL FLATNESS AND GLOBAL RIGIDITY OF HIGHER RANK LATTICE ACTIONS, Transactions of the American Mathematical Society, 349(2), 1997, pp. 657-673
We establish the continuous tangential flatness for orientable weakly
Cartan actions of higher rank lattices. As a corollary, we obtain the
global rigidity of Anosov Cartan actions.