public void deleteMark(Mark mark) {
		marks.remove(mark);
		for (final Connection connection : mark.getConnections()) {
			if (!connection.getA().equals(mark)) {
				connection.getA().deleteConnection(connection);
			}
			if (!connection.getB().equals(mark)) {
				connection.getB().deleteConnection(connection);
			}
			deleteConnection(connection);
		}
	}