[1] G. Chartrand L. Lesniak: Graphs & Digraphs. 2nd Edition. Monterey, CA (1986). MR 0834583

[2] F. Harary: The maximum connectivity of a graph. Proc. Acad. Sci. USA 48 (1962) 1142- 1146. MR 0137663 | Zbl 0115.41003

[3] R. M. Karp: Reducibility among combinatorial problems. Complexity of Computer Computations (eds., R. E. Miller and J. W. Thatcher). Plenum Press, New York (1972) 85-103. MR 0378476

[4] O. R. Oellermann S. Tian: Steiner centers in graphs. J. Graph Theory (to appear). MR 1073100