Editing Glossary of graph theory (section)

==U==
{{glossary}}

{{term|unary vertex}}
{{defn|In a rooted tree, a unary vertex is a vertex which has exactly one child vertex.}}

{{term|undirected}}
{{defn|An [[undirected graph]] is a graph in which the two endpoints of each edge are not distinguished from each other. See also ''directed'' and ''mixed''. In a [[mixed graph]], an undirected edge is again one in which the endpoints are not distinguished from each other.}}

{{term|uniform}}
{{defn|A hypergraph is {{mvar|k}}-uniform when all its edges have {{mvar|k}} endpoints, and uniform when it is {{mvar|k}}-uniform for some {{mvar|k}}. For instance, ordinary graphs are the same as {{math|2}}-uniform hypergraphs.}}

{{term|universal}}
{{defn|no=1|A [[universal graph]] is a graph that contains as subgraphs all graphs in a given family of graphs, or all graphs of a given size or order within a given family of graphs.}}
{{defn|no=2|A [[universal vertex]] (also called an apex or dominating vertex) is a vertex that is adjacent to every other vertex in the graph. For instance, [[wheel graph]]s and connected [[threshold graph]]s always have a universal vertex.}}
{{defn|no=3|In the [[logic of graphs]], a vertex that is [[universal quantifier|universally quantified]] in a formula may be called a universal vertex for that formula.}}

{{term|unweighted graph}}
{{defn|A {{gli|graph}} whose {{gli|vertex|vertices}} and {{gli|edge}}s have not been assigned {{gli|weight}}s; the opposite of a {{gli|weighted graph}}.}}

{{term|utility graph}}
{{defn|The [[utility graph]] is a name for the [[complete bipartite graph]] <math>K_{3,3}</math>.}}

{{glossary end}}