(sorry, couldn't resist)
]]>Let us perhaps close some (pairwise ;D) different things instead.
Yeah, one more question like those other two, and I'll be one of the first to pull the trigger to close.
]]>But, it produces some interesting contributions and OP put a lot of effort in. That it is edited to give an overview of contributions is very good in the long run as it will avoid duplicates.
So, I am in favor of keeping it for a while and voted to reopen. Let us perhaps close some (pairwise ;D) different things instead.
]]>I can see what Eric Wofsey means, but I'm not quite prepared to fully agree. Duality and dichotomy play an important role in human mathematical thought, and I think a case could be made for triality and trichotomy as well (C.S. Peirce was much occupied with 'threeness', and he was no slouch). Once we venture into Jung and quaternities, I think we could safely hit the close button, despite the fact that I find Jung sort of fascinating, generally speaking. :-)
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