(For the [text](url) link syntax to work, you need the full URL, i.e. including the http:// bit at the start: http://comptop.stanford.edu/preprints/heads.pdf)
[text](url)
(For the
[text](url)link syntax to work, you need the full URL, i.e. including the http:// bit at the start: http://comptop.stanford.edu/preprints/heads.pdf)