V18.11 Icosahedron .................................................................................................................. 210
18.12 Stellate regular polyhedra
18.12.1 Number 1 ..................................................................................................................... 211
18.12.2 Number 2 .................................................................................................................... 215
18.12.3 Number 3 ..................................................................................................................... 216
18.12.4 Number 4 ..................................................................................................................... 217
18.13 Pseudorregular polyhedra ............................................................................................ 220
18.13.1 Rhombic-dodecahedron ............................................................................................... 220
18.13.2 Trapezohedron ............................................................................................................. 223
18.14 Macles .......................................................................................................................... 225
Tetrahedral. Made of cubes. Aragonite. Cube-octahedral. Pyrito-
hedra. The iron cross.
19 Round solids ................................................................................................................ 2 33
Sphere. Cylinder. Cone.
20 Paper flexibility.
20.1 Hooke ́s law ................................................................................................................. 236
20.2 The p number.............................................................................................................. 238
21 Quadrics ....................................................................................................................... 241
21.1 Elliptic ellipsoid........................................................................................................... 241
21.2 Cyclic sections deformable ellipsoid (cyclic ellipsoid) ............................................... 242
21.3 Hyperboloid ................................................................................................................. 247
21.4 Hyperbolic paraboloid ................................................................................................. 253
Acknowledgement, Bibliography................................................................................ 257