[1] V. Baláž J. Koča V. Kvasnička M. Sekanina: 
A metric foг gгaphs. Časopis pěst. mat. 111 (1986), 431-433. 
MR 0871718[2] G. Chartrand F. Saba H.-B. Zou: 
Edg eгotations and distance between graphs. Časopis pest. mat. 110 (1985), 87-91. 
MR 0791281[3] F. Kaden: 
Gгaph metrics and distance graphs. In: Graphs and Other Combinatorial Topics. Proc. Symp. Prague 1982 (ed. M. Ғiedler). Teubner Leipzig 1983. 
MR 0737029[4] Z. Miller: 
Contraction of graphs: a theorem of Ore and an extremal problem. Discr. Math. 21(1978), 261-272. 
MR 0522900[5] F. Sobik: 
On some measures of distance between graphs. In: Graphs and Other Combinatorial Topics, Proc. Symp. Prague (ed. M. Fiedler). Teubner Leipzig 1983. 
MR 0737052 | 
Zbl 0528.05056[6] B. Zelinka: 
On a certain distance between isomorphism classes of graphs. Časopis pest. mat. 100 (1975), 371-373. 
MR 0416995 | 
Zbl 0312.05121[7] B. Zelinka: 
A distance between isomorphism classes of trees. Czechoslovak Math. Ј. 33 (1983), 126-130. 
MR 0687425 | 
Zbl 0523.05028[8] B. Zelinka: 
Comparison of various distances between isomorphism classes of graphs. Časopis pěst. mat. 110 (1985), 289-293. 
MR 0808079 | 
Zbl 0579.05056[9] A. A. Zykov: 
On the edge numbeг of graphs with no greater Hadwiger number than 4. Prikl. mat. i progr. 7 (1972), 52-55. 
MR 0309793