Sent this earlier from the incorrect address that was bounced: It's true with roman numerals (considered as topological blobs on paper, and as numerals) that EC(I) = I EC(II)=II EC(III)=III Bill Thurston On Apr 13, 2011, at 4:28 PM, Dan Asimov wrote:

I just got some perplexed requests to clarify how such a trans-categorical equation could even mean anything.

This is a genuine puzzle, but maybe not 100% serious. That's all I'll say.

--Dan

<< PUZZLE: Let EC(X) denote the Euler characteristic of X.

Solve for X:

EC(X) = X

...

...

Sometimes the brain has a mind of its own.

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