[dpassens]

But that's a relative link, so if you're using HN via HTTPS that will be an HTTPS link as well. Downloading the paper redirects you to http://rachit.pl/files/pubs/calyx.pdf, a plain HTTP link.

[chrisjj]

OK. Thanks.

But http://www.bbc.co.uk works.

http://rachit.pl/files/pubs/calyx.pdf fails. I suspect /PDF/.