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Title: On the spectrum problem for some digraphs of order 4 and size 6
Consider the multigraph obtained by adding a double edge to $K_4-e$. Now, let $D$ be a directed graph obtained by orientating the edges of that multigraph. We establish necessary and sufficient conditions on $n$ for the existence of a $(K^{*}_{n},D)$-design for four such orientations.
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Journal of Combinatorial Mathematics and Combinatorial Computing (ISSN: 0835-3026)
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National Science Foundation
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