Abstract

Combinatorially regular polyhedra are polyhedral realizations (embeddings) in Euclidean 3-space E3 of regular maps on (orientable) closed compact surfaces. They are close analogues of the Platonic solids. A surface of genus g ≥ 2 admits only finitely many regular maps, and generally only a small number of them can be realized as polyhedra with convex faces. When the genus g is small, meaning that g is in the historically motivated range 2 ≤ g ≤ 6, only eight regular maps of genus g are known to have polyhedral realizations, two discovered quite recently. These include spectacular convex-faced polyhedra realizing famous maps of Klein, Fricke, Dyck, and Coxeter. We provide supporting evidence that this list is complete; in other words, we strongly conjecture that in addition to those eight there are no other regular maps of genus g, with 2 ≤ g ≤ 6, admitting realizations as convex-faced polyhedra in E3. For all admissible maps in this range, save Gordan’s map of genus 4, and its dual, we rule out realizability by a polyhedron in E3.

Highlights

  • A polyhedron P, for the purpose of this paper, is a closed compact surface in Euclidean 3-spaceE made up from finitely many convex polygons, called the faces of P, such that any two polygons intersect, if at all, in a common vertex or a common edge

  • Since P is embedded in E3, the underlying surface is free of self-intersections and is necessarily orientable; and since the faces of P are convex, the underlying abstract polyhedron is necessarily a lattice, meaning here that any two distinct faces meet, if at all, in a common vertex or a common edge

  • A polyhedron P is said to be combinatorially regular if its combinatorial automorphism group Γ (P ) is transitive on the flags of P

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Summary

Introduction

A polyhedron P , for the purpose of this paper, is a closed compact surface in Euclidean 3-space. A combinatorially regular polyhedron is a polyhedral realization in E3 of a regular map on an orientable surface of some genus g (see [5]). Each such polyhedron or map has a (Schläfli) type {p, q} for some p, q > 3, describing the fact that the faces are p-gons, q meeting at each vertex. There are only finitely many regular maps in this genus range, and we wish to determine those which admit realizations as (convex-faced, combinatorially regular) polyhedra. For a discussion of regular toroidal polyhedra see Schwörbel [21]

The Eight Maps and Their Polyhedra
Klein’s Map
Dyck’s Map
Coxeter’s Geometric Skew Polyhedra
Coxeter’s Topological Analogues of Skew Polyhedra
The Klein–Fricke Map
Completeness of the List
Open Problems
Full Text
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