Conway criterion

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Prototile Octagon satisfying the Conway criterion. Sections AB and ED are shown in red, and the remaining segments are shown in color with a dot on the point of centrosymmetry. Octagon Prototile.svg
Prototile Octagon satisfying the Conway criterion. Sections AB and ED are shown in red, and the remaining segments are shown in color with a dot on the point of centrosymmetry.
A tessellation of the above prototile meeting the Conway criterion. Octagon Prototile Tessellation.svg
A tessellation of the above prototile meeting the Conway criterion.

In the mathematical theory of tessellations, the Conway criterion, named for the English mathematician John Horton Conway, is a sufficient rule for when a prototile will tile the plane. It consists of the following requirements: [1] The tile must be a closed topological disk with six consecutive points A, B, C, D, E, and F on the boundary such that:

Contents

Any prototile satisfying Conway's criterion admits a periodic tiling of the plane—and does so using only 180-degree rotations. [1] The Conway criterion is a sufficient condition to prove that a prototile tiles the plane but not a necessary one. There are tiles that fail the criterion and still tile the plane. [3]

Every Conway tile is foldable into either an isotetrahedron or a rectangle dihedron and conversely, every net of an isotetrahedron or rectangle dihedron is a Conway tile. [4] [3]

History

The Conway criterion applies to any shape that is a closed disk—if the boundary of such a shape satisfies the criterion, then it will tile the plane. Although the graphic artist M.C. Escher never articulated the criterion, he discovered it in the mid 1920s. One of his earliest tessellations, later numbered 1 by him, illustrates his understanding of the conditions in the criterion. Six of his earliest tessellations all satisfy the criterion. In 1963 the German mathematician Heinrich Heesch described the five types of tiles that satisfy the criterion. He shows each type with notation that identifies the edges of a tile as one travels around the boundary: CCC, CCCC, TCTC, TCTCC, TCCTCC, where C means a centrosymmetric edge, and T means a translated edge. [5]

Conway was likely inspired by Martin Gardner's July 1975 column in Scientific American that discussed which convex polygons can tile the plane. [6] In August 1975, Gardner revealed that Conway had discovered his criterion while trying to find an efficient way to determine which of the 108 heptominoes tile the plane. [7]

Examples

Example tessellation based on a Type 1 hexagonal tile. Isohedral tiling p6-3.png
Example tessellation based on a Type 1 hexagonal tile.

In its simplest form, the criterion simply states that any hexagon with a pair of opposite sides that are parallel and congruent will tessellate the plane. [8] In Gardner's article, this is called a type 1 hexagon. [7] This is also true of parallelograms. But the translations that match the opposite edges of these tiles are the composition of two 180° rotations—about the midpoints of two adjacent edges in the case of a hexagonal parallelogon, and about the midpoint of an edge and one of its vertices in the case of a parallelogram. When a tile that satisfies the Conway Criterion is rotated 180° about the midpoint of a centrosymmetric edge, it creates either a generalized parallelogram or a generalized hexagonal parallelogon (these have opposite edges congruent and parallel), so the doubled tile can tile the plane by translations. [4] The translations are the composition of 180° rotations just as in the case of the straight-edge hexagonal parallelogon or parallelograms. [9]

A tiling nonomino that does not satisfy the Conway criterion. Non-Conway tiling nonomino 1.jpg
A tiling nonomino that does not satisfy the Conway criterion.
The four heptominoes incapable of tiling the plane, including the one heptomino with a hole. No Tile Heptominoes.png
The four heptominoes incapable of tiling the plane, including the one heptomino with a hole.

The Conway criterion is surprisingly powerful—especially when applied to polyforms. With the exception of four heptominoes, all polyominoes up through order 7 either satisfy the Conway criterion or two copies can form a patch which satisfies the criterion. [10]

Related Research Articles

<span class="mw-page-title-main">Prototile</span> Basic shape(s) used in a tessellation

In mathematics, a prototile is one of the shapes of a tile in a tessellation.

<span class="mw-page-title-main">Hexagon</span> Shape with six sides

In geometry, a hexagon is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°.

<span class="mw-page-title-main">Polyomino</span> Geometric shapes formed from squares

A polyomino is a plane geometric figure formed by joining one or more equal squares edge to edge. It is a polyform whose cells are squares. It may be regarded as a finite subset of the regular square tiling.

<span class="mw-page-title-main">Kite (geometry)</span> Quadrilateral symmetric across a diagonal

In Euclidean geometry, a kite is a quadrilateral with reflection symmetry across a diagonal. Because of this symmetry, a kite has two equal angles and two pairs of adjacent equal-length sides. Kites are also known as deltoids, but the word deltoid may also refer to a deltoid curve, an unrelated geometric object sometimes studied in connection with quadrilaterals. A kite may also be called a dart, particularly if it is not convex.

A polyiamond is a polyform whose base form is an equilateral triangle. The word polyiamond is a back-formation from diamond, because this word is often used to describe the shape of a pair of equilateral triangles placed base to base, and the initial 'di-' looks like a Greek prefix meaning 'two-'. The name was suggested by recreational mathematics writer Thomas H. O'Beirne in New Scientist 1961 number 1, page 164.

<span class="mw-page-title-main">Tessellation</span> Tiling of a plane in mathematics

A tessellation or tiling is the covering of a surface, often a plane, using one or more geometric shapes, called tiles, with no overlaps and no gaps. In mathematics, tessellation can be generalized to higher dimensions and a variety of geometries.

<span class="mw-page-title-main">Wallpaper group</span> Classification of a two-dimensional repetitive pattern

A wallpaper is a mathematical object covering a whole Euclidean plane by repeating a motif indefinitely, in manner that certain isometries keep the drawing unchanged. For each wallpaper there corresponds a group of congruent transformations, with function composition as the group operation. Thus, a wallpaper group is a mathematical classification of a two‑dimensional repetitive pattern, based on the symmetries in the pattern. Such patterns occur frequently in architecture and decorative art, especially in textiles, tessellations, tiles and physical wallpaper.

<span class="mw-page-title-main">Marjorie Rice</span> American amateur mathematician

Marjorie Ruth Rice was an American amateur mathematician most famous for her discoveries of pentagonal tilings in geometry.

<span class="mw-page-title-main">Polyhex (mathematics)</span> Polyform with a regular hexagon as the base form

In recreational mathematics, a polyhex is a polyform with a regular hexagon as the base form, constructed by joining together 1 or more hexagons. Specific forms are named by their number of hexagons: monohex, dihex, trihex, tetrahex, etc. They were named by David Klarner who investigated them.

In geometry, the Heesch number of a shape is the maximum number of layers of copies of the same shape that can surround it with no overlaps and no gaps. Heesch's problem is the problem of determining the set of numbers that can be Heesch numbers. Both are named for geometer Heinrich Heesch, who found a tile with Heesch number 1 and proposed the more general problem.

<span class="mw-page-title-main">Heptomino</span> Geometric shape formed from seven squares

A heptomino is a polyomino of order 7, that is, a polygon in the plane made of 7 equal-sized squares connected edge-to-edge. The name of this type of figure is formed with the prefix hept(a)-. When rotations and reflections are not considered to be distinct shapes, there are 108 different free heptominoes. When reflections are considered distinct, there are 196 one-sided heptominoes. When rotations are also considered distinct, there are 760 fixed heptominoes.

<span class="mw-page-title-main">Nonomino</span> Geometric shape formed from nine squares

A nonomino is a polyomino of order 9, that is, a polygon in the plane made of 9 equal-sized squares connected edge-to-edge. The name of this type of figure is formed with the prefix non(a)-. When rotations and reflections are not considered to be distinct shapes, there are 1,285 different free nonominoes. When reflections are considered distinct, there are 2,500 one-sided nonominoes. When rotations are also considered distinct, there are 9,910 fixed nonominoes.

<span class="mw-page-title-main">Truncated hexagonal tiling</span>

In geometry, the truncated hexagonal tiling is a semiregular tiling of the Euclidean plane. There are 2 dodecagons (12-sides) and one triangle on each vertex.

<span class="mw-page-title-main">Rhombille tiling</span> Tiling of the plane with 60° rhombi

In geometry, the rhombille tiling, also known as tumbling blocks, reversible cubes, or the dice lattice, is a tessellation of identical 60° rhombi on the Euclidean plane. Each rhombus has two 60° and two 120° angles; rhombi with this shape are sometimes also called diamonds. Sets of three rhombi meet at their 120° angles, and sets of six rhombi meet at their 60° angles.

<span class="mw-page-title-main">Pentagonal tiling</span> A tiling of the plane by pentagons

In geometry, a pentagonal tiling is a tiling of the plane where each individual piece is in the shape of a pentagon.

<span class="mw-page-title-main">Octomino</span> Geometric shape formed from eight squares

An octomino is a polyomino of order 8, that is, a polygon in the plane made of 8 equal-sized squares connected edge-to-edge. When rotations and reflections are not considered to be distinct shapes, there are 369 different free octominoes. When reflections are considered distinct, there are 704 one-sided octominoes. When rotations are also considered distinct, there are 2,725 fixed octominoes.

<span class="mw-page-title-main">Anisohedral tiling</span> Tiling forced to use inequivalent tile placements

In geometry, a shape is said to be anisohedral if it admits a tiling, but no such tiling is isohedral (tile-transitive); that is, in any tiling by that shape there are two tiles that are not equivalent under any symmetry of the tiling. A tiling by an anisohedral tile is referred to as an anisohedral tiling.

<span class="mw-page-title-main">Parallelogon</span> Polygon able to tessellate edge-to-edge, without rotation

In geometry, a parallelogon is a polygon with parallel opposite sides that can tile a plane by translation.

<span class="mw-page-title-main">Rep-tile</span> Shape subdivided into copies of itself

In the geometry of tessellations, a rep-tile or reptile is a shape that can be dissected into smaller copies of the same shape. The term was coined as a pun on animal reptiles by recreational mathematician Solomon W. Golomb and popularized by Martin Gardner in his "Mathematical Games" column in the May 1963 issue of Scientific American. In 2012 a generalization of rep-tiles called self-tiling tile sets was introduced by Lee Sallows in Mathematics Magazine.

<span class="mw-page-title-main">Einstein problem</span> Question about single-shape aperiodic tiling

In plane geometry, the einstein problem asks about the existence of a single prototile that by itself forms an aperiodic set of prototiles; that is, a shape that can tessellate space but only in a nonperiodic way. Such a shape is called an einstein, a word play on ein Stein, German for "one stone".

References

  1. 1 2 Will It Tile? Try the Conway Criterion! by Doris Schattschneider Mathematics Magazine Vol. 53, No. 4 (Sep, 1980), pp. 224-233
  2. Periodic Tiling: Polygons in General
  3. 1 2 Treks Into Intuitive Geometry: The World of Polygons and Polyhedra by Jin Akiyama and Kiyoko Matsunaga, Springer 2016, ISBN   9784431558415
  4. 1 2 Two Conway Geometric Gems , Doris Schattschneider, Nov 1, 2021 [video]
  5. Flächenschluss. System der Formen lückenlos aneinanderschliessender Flachteile , by Heinrich Heesch and Otto Kienzle, Berlin: Springer, 1963.
  6. Gardner, Martin. On tessellating the plane with convex polygon tiles “Mathematical Games” Scientific American, vol. 233, no. 1 (July 1975)
  7. 1 2 Gardner, Martin. More about tiling the plane: the possibilities of polyominoes, polyiamonds, and polyhexes “Mathematical Games” Scientific American, vol. 233, no. 2 (August 1975)
  8. Polyominoes: A Guide to Puzzles and Problems in Tiling, by George Martin, Mathematical Association of America, Washington, DC, 1991, p. 152, ISBN 0-88385-501-1
  9. Drawing Wallpaper Patterns: The five types of Conway Criterion polygon tile, PDF file
  10. Rhoads, Glenn C. (2005). "Planar tilings by polyominoes, polyhexes, and polyiamonds". Journal of Computational and Applied Mathematics. 174 (2): 329–353. doi: 10.1016/j.cam.2004.05.002 .