A monitor for Variable, to observe variable modification (for integer variable : value removals, bounds modification
or instantiation) and do something right after the modification.
This differs from
because it is not scheduled in the propagation engine.
However, it assumes that
executes fast and low complexity operations.
Otherwise, it should be a propagator.
This also differs from
because it is not a specific variable, and can connect
two or more variables together. For instance, this can be used for logging issue.