He was then with the mathematics department at the RAND Corporation until 1971 when he moved to Cornell University as the Maxwell Upson Professor of Engineering.
The mathematical theory of interval graphs was developed with a view towards applications by researchers at the RAND Corporation's mathematics department, which included young researchers—such as Peter C. Fishburn and students like Alan C. Tucker and Joel E. Cohen—besides leaders—such as Delbert Fulkerson and (recurring visitor) Victor Klee.