Delian problem:see geometric problems of antiquitygeometric problems of antiquity,
three famous problems involving elementary geometric constructions with straight edge and compass, conjectured by the ancient Greeks to be impossible but not proved to be so until modern times.
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the problem of the duplication of the cube (fifth century B.C.). The problem consists in constructing, using a compass and a ruler, a cube, the volume of which is twice the volume of the given cube. The name of the problem is connected with a legend, according to which the inhabitants of Delos, in order to escape the plague, had to execute the Delphic oracle’s command of doubling the volume of the altar without changing its cubic form.