A constraint for which the catalogue provides a description in terms of a conjunction of more elementary constraints. This is the case when the constraint is described by one or several graph constraints that all satisfy the following property: the description uses the graph property and forces all arcs of the initial graph to belong to the final graph. Most of the time we have only one single graph constraint. But some constraints (e.g., ) use more than one. Note that the arc constraint can sometimes be a logical expression involving several constraints (e.g., ).