[1] L. Szamkolowicz:
On a classification of graphs with respect to the properties of neighbourhood graphs. Proc. of Combinatorics Conference (Eger, 1981). Finite and Infìnite Sets (A. Hajnal, L. Lovasz, V. T. Sos, eds.), Coll. Math. Soc. J. Bolyai, vol. 37, North-Holland, Amsterdam, Oxford, New York, 1984, 675-678.
MR 0818269
[2] L. Szamkolowicz:
On a conjecture concerning the classification of graphs with respect to the properties of neighbourhood gгaphs. Proc. of the Third Czechoslovak Symposium on Graph Theory (Praha, 1982), Teubner-Texte zur Mathematik, 1983, 307-311.
MR 0737056