2. Definition and notationLet G = (V, E) be a graph. For u, v ∈ V, distG(u, v) denotes the distance between u and v in G. The diameter of G, denotedby diam(G), is the maximum distance between two vertices in G. Let α(G) denote the size of a maximum independent setof G. We denote the complete graph with n vertices by Kn and the complete bipartite graph with two partite sets of sizes mand n by Km,n. The cycle of n vertices is denoted by Cn.For each unit disk graph G = (V, E), there exists a mapping φ : V → R2 such that {u, v} ∈ E if and only if ∥φ(u)−φ(v)∥≤ 1. We call the mapping φ a realization of G. Throughout the paper, a vertex v and its associated point φ(v) are used interchangeably.The x-coordinate and y-coordinate of φ(w) are denoted by φx(w) and φy(w), respectively. The width of φ isdefined as maxu,v∈V |φy(u) − φy(v)|. A realization of width at most c is called a c-realization. We denote ∥φ(u) − φ(v)∥ bydistφ(u, v). The diameter of φ, denoted by diam(φ), is defined as maxu,v∈V ∥φ(u) − φ(v)∥.A graph G = (V, E) is a comparability graph if there is a partial order (V,≤) such that {u, v} ∈ E if and only if u ≤ vor v ≤ u. The complement of a comparability graph is a co-comparability graph. There are a few characterizations of cocomparabilitygraphs. For instance, G = (V, E) is a co-comparability graph if and only if there is a linear ordering (V, <)such that u < v < w and {u,w} ∈ E imply {u, v} ∈ E or {v,w} ∈ E (see [2, Section 4.1]). We call such an ordering aco-comparability ordering. As mentioned before, it is known that G ∈ SG(√3/2) implies that G is a co-comparability graph[2, Section 3.1.2], but the converse does not hold in general (e.g., K1,6).For a, b ∈ R, the closed interval [a, b] is {c ∈ R : a ≤ c ≤ b}, the open interval (a, b) is {c ∈ R : a < c < b}, theclosed–open interval [a, b) is {c ∈ R : a ≤ c < b}, and the open–closed interval (a, b] is {c ∈ R : a < c ≤ b}. A mixedunit interval graph is the intersection graph of a set of closed, open, closed–open, and open–closed unit intervals. The classof mixed unit interval graphs is denoted by MUIG.
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