A. Ko, and B. Myers. Journal of Visual Languages & Computing, 16 (1-2):
41 - 84(2005)<ce:title>2003 IEEE Symposium on Human Centric Computing Languages and Environments</ce:title>.
S. Jacobsen, H. Ko, E. Iversen, and C. Davis. Proceedings of the IEEE International Conference on Robotics and
Automation, page 1334--1339. Scottsdale, AZ, USA, (May 1989)