[1] Farzan M.: Automorphisms of double covers of a graph. CNRS Probl. Comb. et Théorie des Graphes, Orsay 1976, pp. 137-138. CNRS Paris 1978. MR 0539960

[2] Foulis D. J., Randall С. H.: Operational statistics. I. Basic concepts. Math. Physics, Vol. 13, No. 11. Zbl 0287.60002

[3] Waller D. A.: Double covers of graphs. Bull. Austral. Math. Soc. 14 (1976), 233-248. DOI 10.1017/S0004972700025053 | MR 0406876 | Zbl 0318.05113

[4] Zelinka В.: Isotopy od digraphs. Czech. Math. J. 22 (1972), 353-360. MR 0306037

[5] Zelinka В.: On double covers of graphs. Math. Slovaca 32 (1982), 49-54. MR 0648219 | Zbl 0483.05057