[1] Ferdowsi Univ Mashhad, Fac Math Sci, Dept Pure Math, POB 1159-91775, Mashhad, Iran
[2] Ferdowsi Univ Mashhad, Ctr Excellence Anal Algebra Struct, POB 1159-91775, Mashhad, Iran
[3] Inst Teknol Bandung, Combinatorial Math Res Grp, Jl Ganesha 10, Bandung, Indonesia