code: public boolean hasContact(ResidueNumber resNumber1, ResidueNumber resNumber2) {
  		return contacts.containsKey(new Pair<ResidueNumber>(resNumber1, resNumber2));
  	}
docs: Tell whether the given pair is a contact in this GroupContactSet,
  the comparison is done by matching residue numbers and chain identifiers
  @param resNumber1
  @param resNumber2
  @return