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Similarly, a k-isohedral tiling has k separate symmetry orbits (it may contain m different face shapes, for m = k, or only for some m < k). [ 6 ] ("1-isohedral" is the same as "isohedral".) A monohedral polyhedron or monohedral tiling ( m = 1) has congruent faces, either directly or reflectively, which occur in one or more symmetry positions.
Some of the Johnson solids may be categorized as elementary polyhedra, meaning they cannot be separated by a plane to create two small convex polyhedra with regular faces. The Johnson solids satisfying this criteria are the first six— equilateral square pyramid , pentagonal pyramid , triangular cupola , square cupola , pentagonal cupola , and ...
The dual of a non-convex polyhedron is also a non-convex polyhedron. [2] ( By contraposition.) There are ten non-convex isotoxal polyhedra based on the quasiregular octahedron, cuboctahedron, and icosidodecahedron: the five (quasiregular) hemipolyhedra based on the quasiregular octahedron, cuboctahedron, and icosidodecahedron, and their five (infinite) duals:
The icosahedral symmetry can still be maintained with more than 60 subunits, but only in multiples of 60. For example, the T=3 Tomato bushy stunt virus has 60x3 protein subunits (180 copies of the same structural protein). [11] [12] Although these viruses are often referred to as 'spherical', they do not show true mathematical spherical symmetry.
This shape is called a plesiohedron. The tiling generated in this way is isohedral, meaning that it not only has a single prototile ("monohedral") but also that any copy of this tile can be taken to any other copy by a symmetry of the tiling. [1] As with any space-filling polyhedron, the Dehn invariant of a plesiohedron is necessarily zero. [3]
(Definition varies among authors; e.g. some exclude solids with dihedral symmetry, or nonconvex solids.) Uniform if every face is a regular polygon, i.e. it is regular, quasiregular or semi-regular. Semi-uniform if its elements are also isogonal. Scaliform if all the edges are the same length. Noble if it is also isohedral (face-transitive).
It is an isohedral (face-transitive) figure, meaning that all its faces are the same. More specifically, all faces are not merely congruent but also transitive, i.e. lie within the same symmetry orbit. Convex isohedral polyhedra are the shapes that will make fair dice. [1]
All four tilings are 2-isohedral. The chiral pairs of tiles are colored in yellow and green for one isohedral set, and two shades of blue for the other set. The pgg symmetry is reduced to p2 when the chiral pairs are considered distinct. The tiling by type 9 tiles is edge-to-edge, but the others are not. Each primitive unit contains eight tiles.