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Paper IPM / M / 17923 | ||||||||||||||||||
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Abstract: | ||||||||||||||||||
Let Γ=(V(Γ),E(Γ)) be a graph. A subset C of V(Γ) is called a perfect code of Γ, when C is an independent set and
every vertex of V(Γ)∖C
is adjacent to exactly one vertex in C.
Let Γ=\Cay(G,S) be a Cayley graph of a finite group G. A subset C of G is called a perfect code of G, when there exists a Cayley graph Γ of G such that C is a perfect code of Γ.
Recently, groups
whose set of all subgroup perfect codes forms a chain are classified. Also, groups with no proper non-trivial subgroup perfect code are characterized. In this paper,
we generalize it and classify groups whose set of all non-perfect code subgroups forms a chain.
It is proved that if G has a normal Sylow 2-subgroup, then a subgroup H of G is a perfect code of G if and only if its Sylow 2-subgroup is a perfect code of G.
In the rest of this paper, we show that the same result holds for a 2-nilpotent group G, i.e., a subgroup H of a 2-nilpotent group G is a perfect code of G if and only if a Sylow 2-subgroup of H is a perfect code of G.
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