[1] F. Harary R. Z. Norman D. Cartwright: Stгuctural Models. John Wiley & Sons, Inc. New York--London- Sydney 1965. MR 0184874

[2] O. Ore: Theory of Graphs. AMS Colloq. Publ. 38, Providence 1962. MR 0150753 | Zbl 0105.35401