1. Hoàng Xuân Phú, T.D. Long, Orienting Method for Obstacle Problems, Zeitschrift fur Analysis und ihre Anwendungen, Vol. 21, No. 1, pp. 233-248, 2002
2. Hoàng Xuân Phú, Rough Continuity of Linear Operators, Numerical Functional Analysis and Optimization, Vol. 23, No. 1&2, pp. 139-146, 2002