### 3.7.249. Tree

According to the context, the keyword tree has the following meaning:

• In the context of a digraph, a constraint that partitions the vertices of a given initial digraph and that keeps one single successor for each vertex so that each partition corresponds to one tree. Each vertex points to its father or to itself if it corresponds to the root of a tree.

• In the context of an undirected graph a constraint that partitions the vertices of a given initial undirected graph in a set of connected components with no cycles.