"Everything in an encyclopedia is Common Knowledge" - actually true?
Taking the statement “anything in an encyclopedia is common knowledge” at face value reveals it is obviously false. In the comments it was pointed out that half of Americans don’t know what century their civil war was in, but there’s also the fact that two thirds of people worldwide have either not heard of the holocaust or engage in holocaust denial. I recently was in a regional trivia competition with thousands of contestants where I had to explain to the organizers that one of their questions were wrong because they had confused density and mass. Virtually all of the questions on Jeopardy! are answerable if you knew everything in an encyclopedia, but even the specially trained contestants don’t know all the answers. Based on these examples alone, I think the idea that the majority of people know all the facts in most encyclopedias is nonsense.

I would strongly advocate for the idea that encyclopedias are irrelevant to the question of if something should be cited. Besides the fact that the vast majority of people don’t know most of the facts in an encyclopedia, there are other reasons to cite things, including:


Giving credit to the discoverer
Providing a link between your work and previous work on the subject
Making it easier for readers to find similar relevant articles.
Providing accountability for your positions. Sometimes encyclopediae are wrong, and the process of looking for a source would hopefully reveal your mistake.


Even if we pretended that it was common knowledge that every triangle-free graph contains an independent set of size Ω(sqrt(n log n)), all the above reasons to cite that fact would apply.