[1] B. D. ACHARYA M. N. VARTAK: 
On the construction of grapha with given constant valence-difference $(S)$ on each of their lines. Wiss. Z. TH Ilmenau 23 (1977), No 6, 33-60. 
MR 0480187[2] M. BEHZAD G. CHARTRAND: 
Introduction to the theory of graphs. Allyn and Bacon, Boston 1971. 
MR 0432461[3] B. GRÜNBAUM: 
Convex Polytopes. Wiley and Sons, 1967. 
MR 0226496