The Nakajima problem asks if a convex body with constant width and constant brightness must be a Euclidean ball. An affirmative answer is only known in three dimensions(Howard, 2006). A convex body has C^1 boundary if its boundary is locally the graph of a differentiable function. Suppose any C^1 convex body with constant width and constant brightness must be a Euclidean ball. From this, can it be shown that any convex body with constant width and constant brightness must be a ball?

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