[1] Berge Claude: 
Théorie des graphes et ses applications. Russian translation, Moscow 1962. 
MR 0155312 | 
Zbl 0101.16602[2] Neuman František: 
On a certain ordering of the vertices of a tree. Čas. pro pěst. mat., Praha, 89 (1964), p. 323-339. 
MR 0181587[3] Sekanina Milan: 
On an ordering of the set of vertices of a connected graph. Publ. Fac. Sci. Univ. Вrno, Czechoslovakia, No. 412 (1960), p. 137-142. 
MR 0140095[4] Sekanina Milan: 
On an ordering of the vertices of graphs. Čas. pro pěst. mat., Praha, 88 (1963), p. 265-282. 
MR 0181588