public Node[] next() throws IOException {
		buffer = null;
		String line;
		String[] tokens = null;
		while ((line = input.readLine()) != null) {
			linenum++;
			line = line.trim();
			if (line.isEmpty())
				continue;
			tokens = line.split("[\\s\\t]+");
			if (tokens.length < 3) {
				tokens = null;
				continue;
			}
			break;
		}
		if (tokens == null)
			return null;
		parse(tokens);
		return buffer;
	}