[1] M. E. Adams J. Nešetřil, J. Sichler: Quotients of rigid graphs. J. Comb. Th. (B), 30, 3(1981), 351-359. MR 0624551

[2] L. Babai, J. Nešetřil: High chromatic rigid graphs I. In: Coll. Math. Soc. Janos Bolyai H. Combinatoгics, Noгth Holland (1978), 53-60. MR 0519255

[З] Z. Hedrlin, A. Рultr: Symmetric relations (undirected grąphs) with given semigroups. Monatsh. für Math. 69 (1965), 318-322. MR 0188082

[4] P. Hell, J. Nešetřil: Images of rigid graphs. (to appear).

[5] P. Hell, J. Nešetřil: Homomorphisms of graphs and of their orientations. Monatsh. für Math. 85 (1978), 39-48. MR 0495696

[6] P. Hell, J. Nešetřil: Graphs and k-societies. Canad. Math. Bull. 13, 3 (1970), 375-381. MR 0276124

[7] P. Hell, J. Nešetřil: Complexity of H-colorings. (to appear). MR 1047555

[8] E. Mendelsohn: On a technique for representing semigroups as endomorphism semigroups of graphs with given properties. Semigroup Forum 4 (1972), 283-294. MR 0304533 | Zbl 0262.20083

[9] J. Nešetřil: On symmetric and antisymmetric relations. Monatsh. für Math. 76 (1972) 323-327. MR 0318038

[10] J. Nešetřil: Graph theory. SNTL (Prague), 1979 (in Czech).

[11] J. Nešetřil, A. Pultr: On classes of relations and graphs determined by subobjects and factor objects. Discrete Math. 22 (1978), 287-300. MR 0522724

[12] M. Sekanina: On an ordering of the vertices of a connected graph. Publ. Fac. Sci. Univ. Brno, No. 412 (1960), 137-142. MR 0140095