Duda, Richard O., and Peter E. Hart. "Use of Hough Transformation to Detect Lines and Curves in Pictures." Communications of the ACM 15, no. 1 (1972): 11-15.

Hart, Peter E., Nils J. Nilsson, and Bertram Raphael. "A Formal Basis for the Heuristic Determination of Minimum Cost Paths." IEEE Transactions on Systems Science and Cybernetics 4, no. 2 (1968): 100-107.