In graph theory, are undirected graphs assumed to be reflexive? I know that in directed graphs vertices do not point to themselves unless explicitly stated, but what about undirected graphs?
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In general, undirected graphs are not assumed to be reflexive. A lot of graph theory concerns "simple graphs", which are undirected and have no "loops", where a loop is an edge joining a vertex to itself. Unless the presence of loops is explicitly stated, I would assume they're not there.