2DHKSTRA E W. A Note on two Problems in Connexion with Graphs [ J ]. Numerische Math -ematik, 1959 (1) :269 -271.
3HART E P, NILSSON N J, RAPHAEL B. A Formal basis for the Heuristic Dtermination of Minimum Cost Paths[ C]. IEEE Trans. Sci. Cy- hem, 1968, SCC - 4(2) : 100 - 107.