code: public boolean addConnectedDownstreamElementWithCheck( IHillSlope element ) {
          if (PfafstetterNumber.areConnectedDownstream(this.getPfafstetterNumber(), element.getPfafstetterNumber())) {
              downstreamElement = element;
              element.addConnectedUpstreamElementWithCheck(this);
              return true;
          }
          return false;
      }
docs: /* (non-Javadoc)
  @see org.hortonmachine.hmachine.modules.hydrogeomorphology.adige.core.IHillSlope#addConnectedDownstreamElementWithChech(org.hortonmachine.hmachine.modules.hydrogeomorphology.adige.core.HillSlope)