Lune (mathematics)

In plane geometry, a lune is the concave-convex area bounded by two circular arcs, while a convex-convex area is termed a lens. The word "lune" derives from luna, the Latin word for Moon.

Formally, a lune is the relative complement of one disk in another (where they intersect but neither is a subset of the other). Alternatively, if A and B are disks, then ${\displaystyle L=A-A\cap B}$ is a lune.

In the 5th century BC, Hippocrates of Chios showed that certain lunes could be exactly squared by straightedge and compass.

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