D. However, D. ??-=-{s-?, and . ???, (b, r 2 )}, also yields a graph Cay

P. Joseph, L. Bohanon, and . Reid, Finite groups with planar subgroup lattices, J. Algebr. Comb, vol.23, issue.3, pp.207-223, 2006.

S. M. Harold and . Coxeter, The complete enumeration of finite groups of the form

C. Droms, Infinite-ended groups with planar Cayley graphs, Journal of Group Theory, vol.9, issue.4, pp.487-496, 2006.
DOI : 10.1515/JGT.2006.032

URL : http://citeseerx.ist.psu.edu/viewdoc/summary?doi=

A. Georgakopoulos, The planar cubic Cayley graphs, ArXiv e-prints, 2011.

Y. Hao, X. Gao, and Y. Luo, On the Cayley Graphs of Brandt Semigroups, Communications in Algebra, vol.106, issue.8, pp.2874-2883, 2011.
DOI : 10.1080/00927872.2011.568028

A. V. Kelarev, On undirected Cayley graphs, Australas, J. Combin, vol.25, pp.73-78, 2002.

V. Andrei, C. E. Kelarev, and . Praeger, On transitive Cayley graphs of groups and semigroups, European J. Combin, vol.24, issue.1, pp.59-72, 2003.

K. Knauer and U. Knauer, Toroidal embeddings of right groups, Thai J. Math, vol.8, issue.3, pp.483-490, 2010.

U. Knauer, Algebraic Graph Theory. Morphisms, monoids and matrices, de Gruyter Studies in Mathematics, vol.41, 2011.
DOI : 10.1515/9783110255096

H. Maschke, The Representation of Finite Groups, Especially of the Rotation Groups of the Regular Bodies of Three-and Four-Dimensional Space, by Cayley's Color Diagrams, American Journal of Mathematics, vol.18, issue.2, pp.156-194, 1896.
DOI : 10.2307/2369680

G. Sabidussi, On a class of fixed-point-free graphs, Proceedings of the American Mathematical Society, vol.9, issue.5, pp.800-804, 1958.
DOI : 10.1090/S0002-9939-1958-0097068-7

V. Denis and . Solomatin, Direct products of cyclic semigroups admitting a planar Cayley graph, Sibirskie Ehlektronnye Matematicheskie Izvestiya [Siberian Electronic Mathematical Reports, pp.238-252, 2006.

X. Zhang, Clifford semigroups with genus zero, Semigroups, Acts and Categories with Applications to Graphs, Mathematics Studies, vol.3, pp.151-160, 2007.