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Let S (m , e) be a class of numerical semigroups with multiplicity m and embedding dimension e. We call a graph G S an S (m , e) -graph if there exists a numerical semigroup S ∈ S (m , e) with V (G S) = { x : x ∈ g (S) } and E (G S) = { x y ⇔ x + y ∈ S } , where g (S) denotes the gap set of S. The aim of this article is to discuss the planarity of S (m , e) -graphs for some cases where S is an irreducible numerical semigroup. [ABSTRACT FROM AUTHOR]

A total k-rainbow dominating function on a graph G = (V , E) is a function f : V (G) → 2 { 1 , 2 , ... , k } such that (i) ∪ u ∈ N (v) f (u) = { 1 , 2 , ... , k } for every vertex v with f (v) = ∅ , (ii) ∪ u ∈ N (v) f (u) ≠ ∅ for f (v) ≠ ∅ . The weight of a total 2-rainbow dominating function is denoted by ω (f) = ∑ v ∈ V (G) | f (v) | . The total k-rainbow domination number of G is the minimum weight of a total k-rainbow dominating function of G. The minimum total 2-rainbow domination problem (MT2RDP) is to find the total 2-rainbow domination number of the input graph. In this paper, we study the total 2-rainbow domination number of graphs. We prove that the MT2RDP is NP-complete for planar bipartite graphs, chordal bipartite graphs, undirected path graphs and split graphs. Then, a linear-time algorithm is proposed for computing the total k-rainbow domination number of trees. Finally, we study the difference in complexity between MT2RDP and the minimum 2-rainbow domination problem. [ABSTRACT FROM AUTHOR]

A total k -coloring of a graph is an assignment of k colors to its vertices and edges such that no two adjacent or incident elements receive the same color. The total coloring conjecture (TCC) states that every simple graph G has a total Δ G + 2 -coloring, where Δ G is the maximum degree of G. This conjecture has been confirmed for planar graphs with maximum degree at least 7 or at most 5, i.e., the only open case of TCC is that of maximum degree 6. It is known that every planar graph G of Δ G ≥ 9 or Δ G ∈ 7,8 with some restrictions has a total Δ G + 1 -coloring. In particular, in (Shen and Wang, 2009), the authors proved that every planar graph with maximum degree 6 and without 4-cycles has a total 7-coloring. In this paper, we improve this result by showing that every diamond-free and house-free planar graph of maximum degree 6 is totally 7-colorable if every 6-vertex is not incident with two adjacent four cycles or three cycles of size p , q , ℓ for some p , q , ℓ ∈ 3,4,4 , 3,3,4 . [ABSTRACT FROM AUTHOR]