Giotto's O

Near the beginning of the Italian Renaissance, Pope Benedict IX planned to have several paintings done in St. Peter's and sent a courtier out to examine the best artists.

The courtier asked each artist to create a sketch to send to the pope to be evaluated.  When the courtier visited Giotto, now considered to be the first great master of that era, Giotto "took a sheet of paper and a brush dipped in red ... and with a turn of the hand made a circle so even in shape and outline that it was a marvel to behold."

The courtier thought he was being ridiculed; Giotto insisted on sending only that drawing to the Pope.

He won the commission.

Giotto's O is a fantastic symbol of virtuosity.  What would be the equivalent of Giotto's O in other domains?  What would be a simple demonstration of mastery?  

It is easy to imagine equivalents in athletics: Pele juggling a soccer ball, for example.  But what about academic skills?  What would math virtuosity look like?

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