Hyperbolic area bounds an inscribed disc

ID: hyperbolic-area-bounds-an-inscribed-disc

If a domain of finite hyperbolic area contains a hyperbolic disc of radius in curvature , then , hence . For an interior point of a hyperbolic triangle, the open disc with radius equal to its distance from the boundary lies inside the triangle. Its area is at most by Gauss-Bonnet theorem, giving the elementary bound ; this need not be the sharp triangle inradius bound.

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