مهران مطیعی

In this paper we show that if D is a valued F-central division algebra such that its residue division ring is a field, then each soluble-by-finite subgroup of its multiplicative group is soluble with derived length at most 3. We also prove that in some special cases the above bound for the length of the derived series is at most 2. Finally, using some examples we show that if the the residue division ring is not a field then the above resuklts are not true.

A Roman dominating function on a graph G is a labeling f:V(G)→{0,1,2} such that every vertex with label 0 has a neighbor with label 2. A Roman dominating function on a graph G is a labeling f:V(G)→{0,1,2} such that every vertex with label 0 has a neighbor with label 2. A maximal Roman dominating function on a graph G is a Roman dominating function f such that V_0={w ∈V(G)│f(w)=0} is not a dominating set of G. The weight of maximal Roman dominating function is the value w(f)=f(V(G))=∑_(x∈V(G))▒〖f(x).〗 The maximal Roman dominating number γ_mR (G) of a graph G equals the minimum weight of a maximal Roman dominating function on G. In this paper, we continue the study of maximal Roman domination number. First, we characterize all graphs G of order n with g(G)≥6 for which γ_mR (G) =n-2, and then, we consider this property for some graphs with girth at most 5.

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