private void oneStep2() {
		for (ALink link : links) {
			final ANode n1 = link.getNode1();
			final ANode n2 = link.getNode2();
			if (n1.getRow() == Integer.MIN_VALUE && n2.getRow() != Integer.MIN_VALUE) {
				if (n2.getRow() == 0) {
					allDown();
				}
				final int row = n2.getRow() - 1;
				if (row == -1) {
					throw new UnsupportedOperationException();
				}
				n1.setRow(row);
			}
		}
	}