Connected subgraph of a tree
= Connected subgraph of a tree
= Connected subgraphs of a tree
{synonym}
A nonempty connected <subgraph> of a <tree>. Between any two included vertices, it contains the unique tree path: its connectedness supplies a path, and the ambient tree has only one. Such subgraphs satisfy the <Helly property>. They need not contain every descendant of an included vertex in any chosen rooting, unlike the descendant-closed data-structure <subtree> convention.