private static StructuredBlock getPredecessor(StructuredBlock stmt) {
		if (stmt.outer instanceof SequentialBlock) {
			SequentialBlock seq = (SequentialBlock) stmt.outer;
			if (seq.subBlocks[1] == stmt)
				return seq.subBlocks[0];
			else if (seq.outer instanceof SequentialBlock)
				return seq.outer.getSubBlocks()[0];
		}
		return null;
	}