Definition:Circle/Circumference/Concave

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Definition

The concave circumference of a circle $C$ is the circumference $C$ from a point inside $C$.


Also see


Historical Note

The concept of the concave circumference arises in Euclid's The Elements as a way of rigorously specifying the relationship between a point and the circumference of the circle under investigation.

As such it is not specifically defined in Euclid's The Elements, but is tacitly understood.