public List<IPropertyInvestigator> getInvestigators() {
if (investigators == null) {
investigators = new ArrayList<IPropertyInvestigator>();
// initialise from source and target
for (int i = 0; i < source.getInvestigators().size(); i++) {
IPropertyInvestigator s = source.getInvestigators().get(i);
IPropertyInvestigator t = target.getInvestigators().get(i);
investigators.add(new IncreaseAbsolute(s.getName() + "-increase",
new DefaultElementSelector(),
s, t));
}