The APL Vade Mecum

"These cards were kind of a novelty item, something Iverson could hand out at conferences. He created these woodblocks that had the entire #APL language specification on it. You could, in theory, refer to these unique business cards to understand how APL works."

https://www.uvic.ca/library/about-us/news-stories/news/voices-uvic-libraries/durno-historic-computing-lab.php
Thanks @jdd