Given a circular table of diameter 9 feet, which is the minimal number of planks (each 1 foot wide and length greater than 9 feet) needed in order to completely cover the tabletop? Nine parallel planks suffice, but is there a covering using fewer planks if suitably oriented?

This proposition is tantamount to showing that a radial projection is area-preserving (King 1994).

It was solved by an ingenious argument of Bang (1950, 1951).

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