Several readers have sent me similar notes:

Maybe I missed it somewhere along the way, but I’m surprised that the concept of “2 + 2 = 5″ in “1984″ hasn’t been mentioned. It’s mentioned quite often in there. Personally, I’d say it’s more famous than the “Notes from Underground” references, but I supppose that’s a matter of opinion.
Some examples [thanks to http://www.online-literature.com/orwell/1984/ ]:
[Winston Smith writing in his diary]
With the feeling that he was speaking to O’Brien, and also that he was setting forth an important axiom, he wrote: Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
[…]
[during torture session]
’How can I help it?’ he blubbered. ‘How can I help seeing what is in front of my eyes? Two and two are four.’
’Sometimes, Winston. Sometimes they are five. Sometimes they are three. Sometimes they are all of them at once. You must try harder. It is not easy to become sane.’