In geometry, polyhedra are associated into pairs called duals, where the vertices of one correspond to the faces of the other. The dual of the dual is the original polyhedron. The dual of a polyhedron with equivalent vertices is one with equivalent faces, and of one with equivalent edges is another with equivalent edges. So the regular polyhedra — the Platonic solids and Kepler-Poinsot polyhedra — are arranged into dual pairs, with the exception of the regular tetrahedron which is self-dual.
Duality is also sometimes called reciprocity or polarity.
Famous quotes containing the word dual:
“Thee for my recitative,
Thee in the driving storm even as now, the snow, the winter-day
Thee in thy panoply, thy measurd dual throbbing and thy beat
Thy black cylindric body, golden brass and silvery steel,”
—Walt Whitman (18191892)