[1] BERGE, C: The theory of graphs. Methuen, London 1962. Zbl 0097.38903

[2] BOSÁK J.: Gгaphs with unique walks, trails or paths of given lengths. In: Theory and Applications of Graphs in America's Bicentennial Year, Proc. Intern. Conf. Theory and Applic. Graphs (ed. by Y. Alavi and D. R. Lick), to appear.

[3] HARARY F.: Graph Theory. Addison-Wesley, Reading, Massachusets 1969. MR 0256911 | Zbl 0196.27202

[4] HEAP B. R., LYNN M. S.: The structure of powers of nonnegative matrices I, II. J. SIAM Appl. Math., 14, 1966, 610-639, 762-777.

[5] HOFFMAN A. J.: An equation in matrices, research problem 2-11. J. Combinatorial Theory, 2, 1967, 393.

[6] LAM C. W. H.: On rational circulants satisfying $A^2 = dI + \lambda J$. Linear Algebra and Appl., 12, 1975, 139-150. MR 0382023

[7] PLESNÍK J., ZNÁM Š.: Strongly geodetic directed graphs. Acta Fac. Refum Natur. Univ. Comenian. Math., 29, 1974, 29-34. MR 0363991 | Zbl 0291.05106

[8] RYSER H. J.: A generalization of the matrix equation $A^2 = J$. Linear Algebra and Appl., 3, 1970, 451-460. MR 0269674

[9] SCHWARZ Š.: A semigroup treatment of some theorems on non-negative rnatrices. Czechoslovak Math. J., 15 (90), 1965, 212-229. MR 0175919

[10] SCHWARZ Š.: On the semigroup of binary relations on a finite set. Czechoslovak Math. J., 20 (95), 1970, 632-679. MR 0296190 | Zbl 0228.20034

[11] WILSON R. J.: On the adjacency matrix of a graph. In: Combinatorics, Proc. Conf. Oxfoгd 1972. The Institute of Mathematics and Its Applications, Essex 1972, 295-321. MR 0342400