Or get a used paperback for ~$4 from Amazon subsidiary AbeBooks.

That was my guess too, but this one actually isn't. Amazon uses "?ref" for reference (innocuous), and "?tag" for affiliates.

For quick reference, a.co and amzn.com are official shorteners and considered safe. amzn.to links however are third-party and often used to conceal affiliate links.

You're right. Missed that, my bad.

Here you go:

https://www.amazon.com/s/ref=nb_sb_ss_i_3_20?url=search-alia...

Just click the book, then under "Share" click the email button, and you'll see..........

a.co is amazon's in house url shortener....freaking seriously man....