code: public boolean addBridge(BetaBridge bridge) {
  		if (bridge1 == null) {
  			bridge1 = bridge;
  			return true;
  		} else if (bridge1.equals(bridge)) {
  			return true;
  		} else if (bridge2 == null) {
  			bridge2 = bridge;
  			return true;
  		} else if (bridge2.equals(bridge)) {
  			return true;
  		} else { //no space left, cannot add the bridge
  			logger.info("Residue forms more than 2 beta Bridges, "
  					+ "DSSP output might differ in Bridges column.");
  			return false;
  		}
  	}
docs: Adds a Bridge to the residue. Each residue can only store two bridges. If
  the residue contains already two Bridges, the Bridge will not be added
  and the method returns false.
  
  @param bridge
  @return false if the Bridge was not added, true otherwise