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Not according to the author:

> According to intuitionism, mathematical objects are products of our mind, like characters in a novel. I agree, as far as it goes...

> Fictionalism holds that the mathematical universe is a collective fiction, like Star Trek or Game of Thrones.

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Well, different characters behave differently in different novels. How is this like an idea of a circle?

> the Cantor set or the Borel Hierarchy is like the USS Enterprise or the Iron Throne. In fact Star Trek fans talk of the Star Trek universe and GOT fans of Westeros and they talk like these places really exist.

You're right, it feels like quite a loose analogy, and only holds when discussing a "canonical" fictional universe. Still, I'm sympathetic to the idea that when we're talking about a circle we're talking about a shared abstract understanding rather than something which objectively exists.

The pupil in the eye. The sun through the clouds. The craters after an impact. The waves when you drop a rock in water. The section of a bamboo stick... And it gets more evident when you go to microscopic world. Some eggs are perfect spheres, as small bubbles in water. I think circles are a real natural shape. Not an invention. Nature brings us all kind of shapes, some of them are discovered studying living creatures, like the scutoid.

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