Implication, inversion and intersection of planar rational cubic curves: T. W. Sederberg. Department of Civil Engineering, 368 Clyde Building, Brigham Young University, Provo, Utah 84602. D. C. Anderson. School of Mechanical Engineering, Purdue University—CADLAB, West Lafayette, Indiana 47907. R. N. Goldman. Control Data Corporation, Arden Hills, Minnesota 55112. Received August 15, 1984; accepted March 18, 1985