code: public BitSet projectG1(BitSet set) {
          BitSet projection = new BitSet(getFirstGraphSize());
          CDKRNode xNode = null;
  
          for (int x = set.nextSetBit(0); x >= 0; x = set.nextSetBit(x + 1)) {
              xNode = getGraph().get(x);
              projection.set(xNode.getRMap().getId1());
          }
          return projection;
      }
docs: Projects a CDKRGraph bitset on the source graph G1.
  @param  set  CDKRGraph BitSet to project
  @return      The associate BitSet in G1