code: public static boolean isSubset(BitSet bs1, BitSet bs2) {
          BitSet clone = (BitSet) bs1.clone();
          clone.and(bs2);
          if (clone.equals(bs2)) {
              return true;
          }
          return false;
      }
docs: Checks whether all the positive bits in BitSet bs2 occur in BitSet bs1. If
  so, the molecular structure from which bs2 was generated is a possible
  substructure of bs1. <p>
  
  Example: <pre>
  Molecule mol = MoleculeFactory.makeIndole();
  BitSet bs = Fingerprinter.getBitFingerprint(mol);
  Molecule frag1 = MoleculeFactory.makePyrrole();
  BitSet bs1 = Fingerprinter.getBitFingerprint(frag1);
  if (Fingerprinter.isSubset(bs, bs1)) {
  System.out.println("Pyrrole is subset of Indole.");
  }
  </pre>
  
  @param  bs1     The reference BitSet
  @param  bs2     The BitSet which is compared with bs1
  @return         True, if bs2 is a subset of bs1
  @cdk.keyword    substructure search