code: private static boolean isInChain(Group g) {
  		ChemComp chemComp = g.getChemComp();
  
  		if (chemComp==null) {
  			logger.warn("Warning: can't determine PolymerType for group "+g.getResidueNumber()+" ("+g.getPDBName()+"). Will consider it as non-nucleotide/non-protein type.");
  			return false;
  		}
  
  		PolymerType polyType = chemComp.getPolymerType();
  		for (PolymerType protOnlyType: PolymerType.PROTEIN_ONLY) {
  			if (polyType==protOnlyType) return true;
  		}
  		for (PolymerType protOnlyType: PolymerType.POLYNUCLEOTIDE_ONLY) {
  			if (polyType==protOnlyType) return true;
  		}
  
  		return false;
  	}
docs: Returns true if the given group is part of the main chain, i.e. if it is
  a peptide-linked group or a nucleotide
  @param g
  @return