void addHydrogenBond(Atom atom1, Atom atom2, short order, BitSet bsA, BitSet bsB) {
		boolean atom1InSetA = bsA == null || bsA.get(atom1.atomIndex);
		boolean atom1InSetB = bsB == null || bsB.get(atom1.atomIndex);
		boolean atom2InSetA = bsA == null || bsA.get(atom2.atomIndex);
		boolean atom2InSetB = bsB == null || bsB.get(atom2.atomIndex);
		if (atom1InSetA & atom2InSetB || atom1InSetB & atom2InSetA)
			addBond(bondMutually(atom1, atom2, order, (short) 1));
	}