def nb(title, year, url, comment=''):
    """Make a markdown table entry for a jupyter/ipython notebook."""
    urlb = f'/blob/master/ipynb/{url}'
    co = f'[c](https://colab.research.google.com/github/norvig/pytudes{urlb})'
    dn = f'[d](https://beta.deepnote.org/launch?template=python_3.6&url=https%3A%2F%2Fgithub.com%2Fnorvig%2Fpytudes%2Fblob%2Fmaster%2Fipynb%2F{url}) '
    my = f'[m](https://mybinder.org/v2/gh/norvig/pytudes/master?filepath=ipynb%2F{url})'
    nb = f'[n](https://nbviewer.jupyter.org/github/norvig/pytudes{urlb})'
    ti = f'<b><a href="ipynb/{url}" title="{comment}">{title}</a></b>'
    if year == 2020: year = f'<u>{year}</u>'
    return f'| {co} {dn} {my} {nb} | {year} | {ti} |'