code: private static Chain removeSeqResHeterogeneity(Chain c) {
  
  		Chain trimmedChain = new ChainImpl();
  
  		ResidueNumber lastResNum = null;
  
  		for (Group g:c.getAtomGroups()) {
  
  			// note we have to deep copy this, otherwise they stay linked and would get altered in addGroup(g)
  			ResidueNumber currentResNum = new ResidueNumber(
  					g.getResidueNumber().getChainName(),
  					g.getResidueNumber().getSeqNum(),
  					g.getResidueNumber().getInsCode());
  
  			if (lastResNum == null || !lastResNum.equals(currentResNum) ) {
  				trimmedChain.addGroup(g);
  			} else {
  				logger.debug("Removing seqres group because it seems to be repeated in entity_poly_seq, most likely has hetero='y': "+g);
  			}
  
  			lastResNum = currentResNum;
  
  		}
  		return trimmedChain;
  	}
docs: The method will return a new reference to a Chain with any consecutive groups
  having same residue numbers removed.
  This is necessary to solve the microheterogeneity issue in entries like 3u7t (see github issue #160)
  @param c
  @return