Learning by Biasing. - Getachew Hailu; Gerald Sommer (ICRA, 1998)

Integrating symbolic knowledge in reinforcement learning. - Getachew Hailu; Gerald Sommer (SMC, 1998)

Towards real learning robots. - Getachew Hailu (Lang, 1999)

Symbolic structures in numeric reinforcement for learning optimum robot trajectory. - Getachew Hailu (Robotics Auton. Syst., 2001)