# Elemental naming scheme (ConceptTopic, 3)

### From Hi.gher. Space

The **elemental naming scheme** is a method of naming many symmetry groups and uniform polytopes devised mostly by Keiji, though the original idea and root words were suggested by Tamfang. It used Tamfang's name for a long time, but has belatedly (and retroactively) been renamed due to his wish to be disassociated from the modifications made by Keiji.

Classically, polytopes are named after their facet counts, or the facet counts of other polytopes from which they are derived. This, however, can lead to confusion, since the facet counts do not match up between one dimension and another. Furthermore, some such polytopes have unwieldly long names as a result. Under the elemental naming scheme, most polytopes have shorter, simpler names, and immediately convey some important properties about the polytope, such as their symmetry.

## Regular polytopes

The prefixes *pyro-*, *geo-*, *aero-*, *xylo-*, *cosmo-* and *hydro-* are used to refer to the basic symmetries of the 5-cell, 8-cell, 16-cell, 24-cell, 120-cell and 600-cell respectively, as well as the analogous symmetries in higher and lower dimensions. The suffixes *-gon*, *-hedron*, *-choron*, *-teron*, *-peton* and so on are applied to refer to the dimension, just as they are in classic facet-count naming.

The above prefixes clearly come from the classical elements of fire, earth, air and water. However, since there was one extra regular polyhedron, the *cosmo-* prefix (meaning universe) was adopted for the dodecahedron and its analogues. Similarly, the *xylo-* prefix (meaning wood) was adopted for the 24-cell.

Finally, one can refer to a regular polytope and its dual collectively by using the prefixes *stauro-* (meaning cross, for geotopes and aerotopes together) and *rhodo-* (referring to plants with 5-fold symmetry, for cosmotopes and hydrotopes together). Note that because the pyrotopes and xylotopes are self-dual, those prefixes are their own collective terms.

For the full list of possibilities, see the table of regular polytopes by elemental name.

## Uniform polytopes

To extend the naming scheme to the (convex, non-prismatic, Wythoffian) uniform polytopes, one must first notice that they divide into *binary asymmetric* and *binary symmetric* polytopes. The latter are those for which the binary representation of their Dx number is palindromic; the former are those for which it is not. The binary asymmetric polytopes are said to have one parent, which is the regular polytope of the same symmetry it is "closest" to, and the binary symmetric polytopes are said to have two parents, as they are equally close to one parent and its dual (though if the parent is self-dual, both parents are the same). We then name the binary asymmetric polytopes with the same elemental prefix as their parent polytope, and the binary symmetric polytopes with the collective elemental prefix containing their two parents (pyro-, stauro-, xylo- or rhodo-).

To distinguish two polytopes of the same symmetry and different Dx numbers, we then use one or more of the following infixes:

- -
*tomo*-, rings the first two nodes, from 3D up (from*tome*, which was previously being used to refer to the various truncates collectively, and now refers to only the Dx 3 truncate) - -
*canti*-, rings the first and third nodes, from 4D up - -
*runci*-, rings the first and fourth nodes, from 4D up - -
*recti*-, rings the second node only, from 4D up - -
*meso*-, rings the middle node (in odd dimensions) or the middle two nodes (in even dimensions), from 3D up - -
*peri*-, rings the outside nodes, from 3D up (from*peripheral*or*perimeter*, meaning outside, or boundary) - -
*panto*-, rings all nodes, from 3D up (though the 2D case also exists, it simply becomes a regular n-gon with twice the number of sides) (from*pan*, meaning all)

If multiple infixes are used, they are ordered with the last ringed node first. For example, *runci* comes before *canti*, which comes before *tomo*.

For the full list of possibilities in 4D, see the list of uniform polychora.