Complete space-like submanifolds in de Sitter space. Liu, X. — 2001 Acta Mathematica Universitatis Comenianae. New Series
Variational Lyapunov method and stability theory. Lakshmikantham, V.; Liu, X.; Leela, S. — 1998 Mathematical Problems in Engineering
Projective shape manifolds and coplanarity of landmark configurations. A nonparametric approach. Balan, V.; Crane, M.; Patrangenaru, V.; Liu, X. — 2009 Balkan Journal of Geometry and its Applications (BJGA)