@phdthesis {PHD-199103-Zheng-Yang,
type = {Dissertation Defense},
author = {Liu, Zheng-Yang},
title = {Qualitative Reasoning about Physical Systems with Multiple Perspectives},
school = {College of Arts and Sciences, University of Oregon},
month = 3,
year = 1991,
note = {Available at \url{https://www.cs.uoregon.edu/Reports/PHD-199103-Zheng-Yang.pdf}},
}