code: @Override
      public void objectRetracted(ObjectRetractedEvent ore) {
          String name = ore.getPropagationContext().getRuleOrigin().getName();
          if (name.equals("DELETE_PROPOSITION")) {
              Proposition prop = (Proposition) ore.getOldObject();
              LOGGER.log(Level.FINEST, "Deleted proposition {0}", prop);
              prop.accept(this.setDeleteDatePropVisitor);
              this.propsToDelete.add(this.setDeleteDatePropVisitor.getDeleted());
          }
      }
docs: Listens for retracted propositions that were retracted as a result of
  another proposition coming from a data source backend with a non-null
  delete date. Adds them to a list that will be passed to the
  query results handler along with propositions that remain in working
  memory.
  
  @param ore an object retracted event containing the retracted object
  and other metadata.