private BitSet getSpecChain(char chain) {
		boolean caseSensitive = viewer.getChainCaseSensitive();
		if (!caseSensitive)
			chain = Character.toUpperCase(chain);
		BitSet bs = new BitSet();
		for (int i = atomCount; --i >= 0;) {
			char ch = atoms[i].getChainID();
			if (!caseSensitive)
				ch = Character.toUpperCase(ch);
			if (chain == ch)
				bs.set(i);
		}
		return bs;
	}