Steffen's Flexible Polyhedron

Abstract

Steffens polyhedron is able to flex without selfintersection and without distorting any of its faces It has 14 triangular faces 21 edges and 9 vertices Euler had conjectured no polyhedron could flex Cauchy proved that convex polyhedra cannot flex The bellows conjecture proven in 1997 asserts that a flexible polyhedron has constant volume as it is flexed