Iterator relations = container.relationList().iterator();
while (relations.hasNext()) {
IORelation relation = (IORelation) relations.next();
if (relation.linkedSourcePortList().size() > 1) {
throw new IllegalActionException(relation,
"Relation has multiple sources of data,"
+ " which is not allowed in PN."
+ " If you want nondeterministic merge,"
+ " use the NondeterministicMerge actor.");