“…Observe that the complete bipartite graph K m,n is a subgraph of G + H. In the following, we will use the characterization of 1-planar complete multipartite graphs from [4]; the results are contained in Table 1, where the notation of sizes of parts of vertices is the following: a − b means the set a, b ∩ Z (the interval of integers); a− means all integers greater or equal to a. k = 2 K 1−,1 ; K 2−,2 ; K 3−6,3 ; K 4,4 k = 3 K 1−,1,1 ; K 2−6,2,1 ; K 2−4,2,2 ; K 3,3,1 k = 4 K 1−6,1,1,1 ; K 2−3,2,1,1 ; K 2,2,2,1−2 k = 5 K 1−2,1−2,1,1,1 k = 6 K 1,1,1,1,1,1 These results imply that G + H is not 1-planar if m ≥ 5, n ≥ 4 or m ≥ 7, n ≥ 3.…”