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Returns True if G is a tree.

A tree is a connected graph with no undirected cycles.

For directed graphs, G is a tree if the underlying graph is a tree. The underlying graph is obtained by treating each directed edge as a single undirected edge in a multigraph.

Parameters:G (graph) – The graph to test.
Returns:b – A boolean that is True if G is a tree.
Return type:bool


In another convention, a directed tree is known as a polytree and then tree corresponds to an arborescence.