Historically you would use the umlaut (lit. re-sound in German) to signify that both vowels are pronounced separately and not as a diphthong! I think some publications, like The New Yorker, are pretentious enough to still use it… In this case, cooperate would be spelled coöperate.

Edit: Oops! Meant to reply to Geek_King

Or non-stick!

I work at an insurance company, and our core business system is written in RPG. We are starting the process of splitting it up and modernizing it, but I suspect there will still be some RPG code running in production in ten years.

No, no! Salad Theory is clearly the only acceptable foodstuff categorization theory.