A wallpaper is a mathematical object covering a whole
Euclidean plane
In mathematics, the Euclidean plane is a Euclidean space of dimension two. That is, a geometric setting in which two real quantities are required to determine the position of each point ( element of the plane), which includes affine notions ...
by repeating a motif indefinitely, in manner that certain
isometries keep the
drawing unchanged. To a given wallpaper there corresponds
a group of such
congruent transformations, with
function composition
In mathematics, function composition is an operation that takes two functions and , and produces a function such that . In this operation, the function is applied to the result of applying the function to . That is, the functions and ...
as the group operation. Thus, a wallpaper group (or plane symmetry group or plane crystallographic group) is in a mathematical classification of a
two‑dimensional repetitive pattern, based on the
symmetries in the pattern. Such patterns occur frequently in
architecture
Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing buildings ...
and
decorative art, especially in
textile
Textile is an Hyponymy and hypernymy, umbrella term that includes various Fiber, fiber-based materials, including fibers, yarns, Staple (textiles)#Filament fiber, filaments, Thread (yarn), threads, different #Fabric, fabric types, etc. At f ...
s,
tessellation
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 ...
s and
tiles as well as
wallpaper.
What this page calls pattern
Any periodic
tiling can be seen as a wallpaper. More particularly, we can consider as a wallpaper a tiling by identical tiles edge‑to‑edge, necessarily periodic, and conceive from it a wallpaper by decorating in the same manner every tiling element, and eventually erase partly or entirely the boundaries between these tiles. Conversely, from every wallpaper we can construct such a tiling by identical tiles edge‑to‑edge, which bear each identical ornaments, the identical outlines of these tiles being not necessarily visible on the original wallpaper. Such repeated boundaries delineate a ''repetitive surface'' added here in dashed lines.
Such pseudo‑tilings connected to a given wallpaper are in infinite number. For example image 1 shows two models of repetitive
squares in two different positions, which have
Another ''repetitive'' square has an
We could indefinitely conceive such repetitive squares larger and larger. An infinity of shapes of repetitive zones are possible for this
Pythagorean tiling, in an infinity of positions on this wallpaper. For example in red on the bottom right‑hand corner of image 1, we could glide its repetitive
parallelogram
In Euclidean geometry, a parallelogram is a simple (non- self-intersecting) quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of eq ...
in one or another position. In common on the first two images: a repetitive square
concentric
In geometry, two or more objects are said to be concentric, coaxal, or coaxial when they share the same center or axis. Circles, regular polygons and regular polyhedra, and spheres may be concentric to one another (sharing the same center p ...
with each small square tile, their common center being a
point symmetry of the wallpaper.
Between identical tiles edge‑to‑edge, an edge is not necessarily a
segment of right line. On the top left‑hand corner of image 3, point ''C '' is a vertex of a repetitive pseudo‑
rhombus with thick stripes on its whole surface, called pseudo‑rhombus because of a concentric repetitive rhombus
constructed from it by taking out a bit of surface somewhere to append it elsewhere, and keep the
area
Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape or planar lamina, while '' surface area'' refers to the area of an op ...
unchanged. By the same process on image 3, a repetitive regular hexagon filled with vertical stripes is constructed from a
rhombic repetitive zone
Conversely, from elementary geometric tiles edge‑to‑edge, an artist like
M. C. Escher created attractive surfaces many times repeated. On image 2,
the minimum area of a repetitive surface by disregarding colors, each repetitive zone in dashed lines consisting of five pieces in a certain arrangement, to be either a square or a
hexagon
In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°.
Regular hexagon
A '' regular hexagon'' has ...
, like in a proof of the
Pythagorean theorem.
In the present article, a ''pattern'' is a repetitive parallelogram of minimal
area
Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape or planar lamina, while '' surface area'' refers to the area of an op ...
in a determined position on the wallpaper. Image 1 shows two parallelogram‑shaped patterns — a square is a particular parallelogram —. Image 3 shows rhombic patterns — a rhombus is a particular parallelogram —.
On this page, all repetitive patterns (of minimal area) are constructed from two
translations that
generate the group of all translations under which the wallpaper is
invariant. With the circle shaped symbol ⵔ of
function composition, a pair like
or
generates the
group of all translations that
transform the Pythagorean tiling into itself.
Possible groups linked to a pattern
A wallpaper remains on the whole unchanged under certain
isometries, starting with certain translations that confer on the wallpaper a repetitive nature. One of the reasons to be unchanged under certain translations is that it covers the whole plane. No mathematical object in our minds is stuck onto a motionless wall! On the contrary an observer or his eye is motionless in front of a
transformation, which glides or
rotates or
flips a wallpaper, eventually could distort it, but that would be out of our subject.
If an isometry leaves unchanged a given wallpaper, then the inverse isometry keeps it also unchanged, like translation
on image 1, 3 or 4, or a ± 120° rotation around a point like ''S '' on image 3 or 4. If they have both this property to leave unchanged a wallpaper, two isometries
composed in one or the other order have then this same property to leave unchanged the wallpaper. To be exhaustive about the concepts of
group and
subgroups under the function composition, represented by the circle shaped symbol ⵔ, here is a traditional
truism A truism is a claim that is so obvious or self-evident as to be hardly worth mentioning, except as a reminder or as a rhetorical or literary device, and is the opposite of falsism.
In philosophy, a sentence which asserts incomplete truth conditio ...
in mathematics: everything remains itself under the
identity transformation. This
identity function
Graph of the identity function on the real numbers
In mathematics, an identity function, also called an identity relation, identity map or identity transformation, is a function that always returns the value that was used as its argument, un ...
can be called translation of
zero vector or rotation of 360°.
A glide can be represented by one or several arrows if parallel and of same length and same sense, in same way a wallpaper can be represented either by a few patterns or by only one pattern, considered as a pseudo‑tile imagined repeated edge‑to‑edge with an infinite number of replicas. Image 3 shows two patterns with two different contents, and the one in dark dashed lines or one of its images under
represents the same wallpaper on the following image 4, by disregarding the colors. Certainly a color is perceived subjectively whereas a wallpaper is an ideal object, however any color can be seen as a label that characterizes certain surfaces, we might think of a
hexadecimal code of color as a label specific to certain zones. It may be added that a
well‑known theorem deals with colors.
Groups are registered in the catalog by examining properties of a parallelogram, edge‑to‑edge with its replicas. For example its diagonals intersect at their common midpoints, center and symmetry point of any parallelogram, not necessarily symmetry point of its content. Other example, the midpoint of a full side shared by two patterns is the center of a new repetitive parallelogram formed by the two together, center which is not necessarily symmetry point of the content of this double parallelogram. Other possible symmetry point, two patterns symmetric one to the other with respect to their common vertex form together a new repetitive surface, the center of which is not necessarily symmetry point of its content.
Certain rotational symmetries are possible only for certain shapes of pattern. For example on
image 2, a Pythagorean tiling is sometimes called pinwheel tilings because of its rotational symmetry of 90 degrees about the center of a tile, either small or large, or about the center of any replica of tile, of course. Also when two equilateral triangles form edge‑to‑edge a rhombic pattern, like on image 4 or 5 (future image 5), a rotational symmetry of 120 degrees about a vertex of a 120° angle, formed by two sides of pattern, is not always a symmetry point of the content of the regular hexagon formed by three patterns together sharing a vertex, because they does not always contain the same motif.
First examples of groups
The simplest wallpaper group, Group ''p''1, applies when there is no symmetry other than the fact that a pattern repeats over regular intervals in two dimensions, as shown in the section on p1 below.
The following examples are patterns with more forms of symmetry:
Image:Wallpaper_group-p4m-2.jpg, Example A: Cloth, Tahiti
Image:Wallpaper_group-p4m-1.jpg, Example B: Ornamental painting, Nineveh
Nineveh (; akk, ; Biblical Hebrew: '; ar, نَيْنَوَىٰ '; syr, ܢܝܼܢܘܹܐ, Nīnwē) was an ancient Assyrian city of Upper Mesopotamia, located in the modern-day city of Mosul in northern Iraq. It is located on the eastern ba ...
, Assyria
Assyria ( Neo-Assyrian cuneiform: , romanized: ''māt Aššur''; syc, ܐܬܘܪ, ʾāthor) was a major ancient Mesopotamian civilization which existed as a city-state at times controlling regional territories in the indigenous lands of the A ...
Image:Wallpaper_group-p4g-2.jpg, Example C: Painted porcelain
Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises main ...
, China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
Examples A and B have the same wallpaper group; it is called
''p''4''m'' in the
IUCr notation and
*442 in the
orbifold notation. Example C has a different wallpaper group, called
''p''4''g'' or
4*2 . The fact that A and B have the same wallpaper group means that they have the same symmetries, regardless of details of the designs, whereas C has a different set of symmetries despite any superficial similarities.
The number of symmetry groups depends on the number of dimensions in the patterns. Wallpaper groups apply to the two-dimensional case, intermediate in complexity between the simpler
frieze groups and the three-dimensional
space groups. Subtle differences may place similar patterns in different groups, while patterns that are very different in style, color, scale or orientation may belong to the same group.
A
proof that there are only 17 distinct
groups
A group is a number of persons or things that are located, gathered, or classed together.
Groups of people
* Cultural group, a group whose members share the same cultural identity
* Ethnic group, a group whose members share the same ethnic ide ...
of such planar symmetries was first carried out by
Evgraf Fedorov in 1891 and then derived independently by
George Pólya in 1924. The proof that the list of wallpaper groups is complete only came after the much harder case of space groups had been done. The seventeen possible wallpaper groups are listed below in .
Symmetries of patterns
A
symmetry
Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definiti ...
of a pattern is, loosely speaking, a way of transforming the pattern so that it looks exactly the same after the transformation. For example,
translational symmetry is present when the pattern can be
translated
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
(in other words, shifted) some finite distance and appear unchanged. Think of shifting a set of vertical stripes horizontally by one stripe. The pattern is unchanged. Strictly speaking, a true symmetry only exists in patterns that repeat exactly and continue indefinitely. A set of only, say, five stripes does not have translational symmetry—when shifted, the stripe on one end "disappears" and a new stripe is "added" at the other end. In practice, however, classification is applied to finite patterns, and small imperfections may be ignored.
The types of transformations that are relevant here are called
Euclidean plane isometries. For example:
* If one ''shifts'' example B one unit to the right, so that each square covers the square that was originally adjacent to it, then the resulting pattern is ''exactly the same'' as the starting pattern. This type of symmetry is called a
translation
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
. Examples A and C are similar, except that the smallest possible shifts are in diagonal directions.
* If one ''turns'' example B clockwise by 90°, around the centre of one of the squares, again one obtains exactly the same pattern. This is called a
rotation. Examples A and C also have 90° rotations, although it requires a little more ingenuity to find the correct centre of rotation for C.
* One can also ''flip'' example B across a horizontal axis that runs across the middle of the image. This is called a
reflection. Example B also has reflections across a vertical axis, and across two diagonal axes. The same can be said for A.
However, example C is ''different''. It only has reflections in horizontal and vertical directions, ''not'' across diagonal axes. If one flips across a diagonal line, one does ''not'' get the same pattern back, but the original pattern shifted across by a certain distance. This is part of the reason that the wallpaper group of A and B is different from the wallpaper group of C.
Another transformation is "Glide", a combination of reflection and translation parallel to the line of reflection.
Formal definition and discussion
Mathematically, a wallpaper group or plane crystallographic group is a type of
topologically discrete group of
isometries of the Euclidean plane that contains two
linearly independent translation
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
s.
Two such
isometry groups are of the same type (of the same wallpaper group) if they are
the same up to an affine transformation of the plane. Thus e.g. a translation of the plane (hence a translation of the mirrors and centres of rotation) does not affect the wallpaper group. The same applies for a change of angle between translation vectors, provided that it does not add or remove any symmetry (this is only the case if there are no mirrors and no
glide reflection
In 2-dimensional geometry, a glide reflection (or transflection) is a symmetry operation that consists of a reflection over a line and then translation along that line, combined into a single operation. The intermediate step between reflecti ...
s, and
rotational symmetry
Rotational symmetry, also known as radial symmetry in geometry, is the property a shape has when it looks the same after some rotation by a partial turn. An object's degree of rotational symmetry is the number of distinct orientations in which ...
is at most of order 2).
Unlike in
the three-dimensional case, one can equivalently restrict the affine transformations to those that preserve
orientation.
It follows from the Bieberbach theorem that all wallpaper groups are different even as abstract groups (as opposed to e.g.
frieze groups, of which two are isomorphic with Z).
2D patterns with double translational symmetry can be categorized according to their
symmetry group type.
Isometries of the Euclidean plane
Isometries of the Euclidean plane fall into four categories (see the article
Euclidean plane isometry for more information).
*
Translation
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
s, denoted by ''T''
''v'', where ''v'' is a
vector in R
2. This has the effect of shifting the plane applying
displacement vector ''v''.
*
Rotations, denoted by ''R''
''c'',''θ'', where ''c'' is a point in the plane (the centre of rotation), and ''θ'' is the angle of rotation.
*
Reflections, or mirror isometries, denoted by ''F''
''L'', where ''L'' is a line in R
2. (''F'' is for "flip"). This has the effect of reflecting the plane in the line ''L'', called the reflection axis or the associated mirror.
*
Glide reflection
In 2-dimensional geometry, a glide reflection (or transflection) is a symmetry operation that consists of a reflection over a line and then translation along that line, combined into a single operation. The intermediate step between reflecti ...
s, denoted by ''G''
''L'',''d'', where ''L'' is a line in R
2 and ''d'' is a distance. This is a combination of a reflection in the line ''L'' and a translation along ''L'' by a distance ''d''.
The independent translations condition
The condition on linearly independent translations means that there exist linearly independent vectors ''v'' and ''w'' (in R
2) such that the group contains both ''T''
''v'' and ''T''
''w''.
The purpose of this condition is to distinguish wallpaper groups from
frieze groups, which possess a translation but not two linearly independent ones, and from
two-dimensional discrete point groups, which have no translations at all. In other words, wallpaper groups represent patterns that repeat themselves in ''two'' distinct directions, in contrast to frieze groups, which only repeat along a single axis.
(It is possible to generalise this situation. One could for example study discrete groups of isometries of R
''n'' with ''m'' linearly independent translations, where ''m'' is any integer in the range 0 ≤ ''m'' ≤ ''n''.)
The discreteness condition
The discreteness condition means that there is some positive real number ε, such that for every translation ''T''
''v'' in the group, the vector ''v'' has length ''at least'' ε (except of course in the case that ''v'' is the zero vector, but the independent translations condition prevents this, since any set that contains the zero vector is linearly dependent by definition and thus disallowed).
The purpose of this condition is to ensure that the group has a compact fundamental domain, or in other words, a "cell" of nonzero, finite area, which is repeated through the plane. Without this condition, one might have for example a group containing the translation ''T''
''x'' for every
rational number
In mathematics, a rational number is a number that can be expressed as the quotient or fraction of two integers, a numerator and a non-zero denominator . For example, is a rational number, as is every integer (e.g. ). The set of all ra ...
''x'', which would not correspond to any reasonable wallpaper pattern.
One important and nontrivial consequence of the discreteness condition in combination with the independent translations condition is that the group can only contain rotations of order 2, 3, 4, or 6; that is, every rotation in the group must be a rotation by 180°, 120°, 90°, or 60°. This fact is known as the
crystallographic restriction theorem, and can be generalised to higher-dimensional cases.
Notations for wallpaper groups
Crystallographic notation
Crystallography has 230
space groups to distinguish, far more than the 17 wallpaper groups, but many of the symmetries in the groups are the same. Thus one can use a similar notation for both kinds of groups, that of
Carl Hermann and
Charles-Victor Mauguin. An example of a full wallpaper name in Hermann-Mauguin style (also called
IUCr notation) is
''p''31''m'', with four letters or digits; more usual is a shortened name like
''cmm'' or
''pg''.
For wallpaper groups the full notation begins with either ''p'' or ''c'', for a ''
primitive cell'' or a ''face-centred cell''; these are explained below. This is followed by a digit, ''n'', indicating the highest order of rotational symmetry: 1-fold (none), 2-fold, 3-fold, 4-fold, or 6-fold. The next two symbols indicate symmetries relative to one translation axis of the pattern, referred to as the "main" one; if there is a mirror perpendicular to a translation axis that is the main one (or if there are two, one of them). The symbols are either ''m'', ''g'', or 1, for mirror, glide reflection, or none. The axis of the mirror or glide reflection is perpendicular to the main axis for the first letter, and either parallel or tilted 180°/''n'' (when ''n'' > 2) for the second letter. Many groups include other symmetries implied by the given ones. The short notation drops digits or an ''m'' that can be deduced, so long as that leaves no confusion with another group.
A primitive cell is a minimal region repeated by lattice translations. All but two wallpaper symmetry groups are described with respect to primitive cell axes, a coordinate basis using the translation vectors of the lattice. In the remaining two cases symmetry description is with respect to centred cells that are larger than the primitive cell, and hence have internal repetition; the directions of their sides is different from those of the translation vectors spanning a primitive cell. Hermann-Mauguin notation for crystal
space groups uses additional cell types.
;Examples
*
''p''2 (''p''2): Primitive cell, 2-fold rotation symmetry, no mirrors or glide reflections.
*
''p''4''gm'' (''p''4''mm''): Primitive cell, 4-fold rotation, glide reflection perpendicular to main axis, mirror axis at 45°.
*
''c''2''mm'' (''c''2''mm''): Centred cell, 2-fold rotation, mirror axes both perpendicular and parallel to main axis.
*
''p''31''m'' (''p''31''m''): Primitive cell, 3-fold rotation, mirror axis at 60°.
Here are all the names that differ in short and full notation.
:
The remaining names are
''p''1,
''p''2,
''p''3,
''p''3''m''1,
''p''31''m'',
''p''4, and
''p''6.
Orbifold notation
Orbifold notation for wallpaper groups, advocated by
John Horton Conway (Conway, 1992) (Conway 2008), is based not on crystallography, but on topology. One can fold the infinite periodic tiling of the plane into its essence, an
orbifold, then describe that with a few symbols.
*A digit, ''n'', indicates a centre of ''n''-fold rotation corresponding to a cone point on the orbifold. By the crystallographic restriction theorem, ''n'' must be 2, 3, 4, or 6.
*An asterisk, *, indicates a mirror symmetry corresponding to a boundary of the orbifold. It interacts with the digits as follows:
*#Digits before * denote centres of pure rotation (
cyclic
Cycle, cycles, or cyclic may refer to:
Anthropology and social sciences
* Cyclic history, a theory of history
* Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr.
* Social cycle, various cycles in so ...
).
*#Digits after * denote centres of rotation with mirrors through them, corresponding to "corners" on the boundary of the orbifold (
dihedral).
*A cross, ×, occurs when a glide reflection is present and indicates a crosscap on the orbifold. Pure mirrors combine with lattice translation to produce glides, but those are already accounted for so need no notation.
*The "no symmetry" symbol, o, stands alone, and indicates there are only lattice translations with no other symmetry. The orbifold with this symbol is a torus; in general the symbol o denotes a handle on the orbifold.
The group denoted in crystallographic notation by
''cmm'' will, in Conway's notation, be 2*22. The 2 before the * says there is a 2-fold rotation centre with no mirror through it. The * itself says there is a mirror. The first 2 after the * says there is a 2-fold rotation centre on a mirror. The final 2 says there is an independent second 2-fold rotation centre on a mirror, one that is not a duplicate of the first one under symmetries.
The group denoted by
''pgg'' will be 22×. There are two pure 2-fold rotation centres, and a glide reflection axis. Contrast this with
''pmg'', Conway 22*, where crystallographic notation mentions a glide, but one that is implicit in the other symmetries of the orbifold.
Coxeter's
bracket notation is also included, based on reflectional
Coxeter groups, and modified with plus superscripts accounting for rotations,
improper rotations and translations.
Why there are exactly seventeen groups
An orbifold can be viewed as a
polygon
In geometry, a polygon () is a plane figure that is described by a finite number of straight line segments connected to form a closed '' polygonal chain'' (or ''polygonal circuit''). The bounded plane region, the bounding circuit, or the two ...
with face, edges, and vertices which can be unfolded to form a possibly infinite set of polygons which tile either the
sphere
A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the c ...
, the plane or the
hyperbolic plane
In mathematics, hyperbolic geometry (also called Lobachevskian geometry or Bolyai– Lobachevskian geometry) is a non-Euclidean geometry. The parallel postulate of Euclidean geometry is replaced with:
:For any given line ''R'' and point ' ...
. When it tiles the plane it will give a wallpaper group and when it tiles the sphere or hyperbolic plane it gives either a
spherical symmetry group or
Hyperbolic symmetry group. The type of space the polygons tile can be found by calculating the
Euler characteristic, ''χ'' = ''V'' − ''E'' + ''F'', where ''V'' is the number of corners (vertices), ''E'' is the number of edges and ''F'' is the number of faces. If the Euler characteristic is positive then the orbifold has an elliptic (spherical) structure; if it is zero then it has a parabolic structure, i.e. a wallpaper group; and if it is negative it will have a hyperbolic structure. When the full set of possible orbifolds is enumerated it is found that only 17 have Euler characteristic 0.
When an orbifold replicates by symmetry to fill the plane, its features create a structure of vertices, edges, and polygon faces, which must be consistent with the Euler characteristic. Reversing the process, one can assign numbers to the features of the orbifold, but fractions, rather than whole numbers. Because the orbifold itself is a quotient of the full surface by the symmetry group, the orbifold Euler characteristic is a quotient of the surface Euler characteristic by the
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
of the symmetry group.
The orbifold Euler characteristic is 2 minus the sum of the feature values, assigned as follows:
*A digit ''n'' without or before a * counts as .
*A digit ''n'' after a * counts as .
*Both * and × count as 1.
*The "no symmetry" o counts as 2.
For a wallpaper group, the sum for the characteristic must be zero; thus the feature sum must be 2.
;Examples
*632: + + = 2
*3*3: + 1 + = 2
*4*2: + 1 + = 2
*22×: + + 1 = 2
Now enumeration of all wallpaper groups becomes a matter of arithmetic, of listing all feature strings with values summing to 2.
Feature strings with other sums are not nonsense; they imply non-planar tilings, not discussed here. (When the orbifold Euler characteristic is negative, the tiling is
hyperbolic; when positive,
spherical or ''
bad'').
Guide to recognizing wallpaper groups
To work out which wallpaper group corresponds to a given design, one may use the following table.
See also
this overview with diagrams.
The seventeen groups
Each of the groups in this section has two cell structure diagrams, which are to be interpreted as follows (it is the shape that is significant, not the colour):
On the right-hand side diagrams, different equivalence classes of symmetry elements are colored (and rotated) differently.
The brown or yellow area indicates a
fundamental domain
Given a topological space and a group acting on it, the images of a single point under the group action form an orbit of the action. A fundamental domain or fundamental region is a subset of the space which contains exactly one point from each o ...
, i.e. the smallest part of the pattern that is repeated.
The diagrams on the right show the cell of the
lattice corresponding to the smallest translations; those on the left sometimes show a larger area.
Group ''p''1 (o)
* Orbifold signature:
o
* Coxeter notation (rectangular):
+,2,∞+">infin;+,2,∞+or
infin;sup>+×
infin;sup>+
* Lattice: oblique
* Point group: C
1
* The group ''p''1 contains only translations; there are no rotations, reflections, or glide reflections.
;Examples of group ''p''1
Image:WallpaperP1.GIF, Computer generated
Image:Wallpaper_group-p1-3.jpg, Medieval
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
wall diapering
The two translations (cell sides) can each have different lengths, and can form any angle.
Group ''p''2 (2222)
* Orbifold signature:
2222
* Coxeter notation (rectangular):
infin;,2,∞sup>+
* Lattice: oblique
* Point group: C
2
* The group ''p''2 contains four rotation centres of order two (180°), but no reflections or glide reflections.
;Examples of group ''p''2
Image:WallpaperP2.GIF, Computer generated
Image:Wallpaper_group-p2-1.jpg, Cloth, Sandwich Islands (Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
)
Image:Wallpaper_group-p2-2.jpg, Mat on which an Egyptian king stood
Image:Wallpaper_group-p2-2 detail 2.jpg, Egyptian mat (detail)
Image:Wallpaper_group-p2-3.jpg, Ceiling of an Egyptian tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
Image:Wallpaper_group-p2-4.jpg, Wire fence, U.S.
Group ''pm'' (**)
* Orbifold signature:
**
* Coxeter notation:
+">infin;,2,∞+or
+,2,∞">infin;+,2,∞* Lattice: rectangular
* Point group: D
1
* The group ''pm'' has no rotations. It has reflection axes, they are all parallel.
;Examples of group ''pm''
(The first three have a vertical symmetry axis, and the last two each have a different diagonal one.)
Image:WallpaperPM.gif, Computer generated
Image:Wallpaper_group-pm-3.jpg, Dress of a figure in a tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
at Biban el Moluk, Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...
Image:Wallpaper_group-pm-4.jpg, Egyptian tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
, Thebes
Image:Wallpaper_group-pm-1.jpg, Ceiling of a tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
at Gourna, Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...
. Reflection axis is diagonal
Image:Wallpaper_group-pm-5.jpg, India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
n metalwork at the Great Exhibition in 1851. This is almost ''pm'' (ignoring short diagonal lines between ovals motifs, which make it ''p''1)
Group ''pg'' (××)
* Orbifold signature:
××
* Coxeter notation:
+,∞+">∞,2)+,∞+or
+,(2,∞)+">infin;+,(2,∞)+* Lattice: rectangular
* Point group: D
1
* The group ''pg'' contains glide reflections only, and their axes are all parallel. There are no rotations or reflections.
;Examples of group ''pg''
Image:WallpaperPG.GIF, Computer generated
Image:Wallpaper_group-pg-1.jpg, Mat with herringbone pattern on which Egyptian king stood
Image:Wallpaper_group-pg-1 detail.jpg, Egyptian mat (detail)
Image:Wallpaper_group-pg-2.jpg, Pavement with herringbone pattern in Salzburg
Salzburg (, ; literally "Salt-Castle"; bar, Soizbuag, label=Austro-Bavarian) is the fourth-largest city in Austria. In 2020, it had a population of 156,872.
The town is on the site of the Roman settlement of ''Iuvavum''. Salzburg was founded ...
. Glide reflection axis runs northeast–southwest
Image:Tile 33434.svg, One of the colorings of the snub square tiling; the glide reflection lines are in the direction upper left / lower right; ignoring colors there is much more symmetry than just ''pg'', then it is ''p''4''g'' (see there for this image with equally colored triangles)[If one thinks of the squares as the background, then one can see a simple patterns of rows of rhombuses.]
Without the details inside the zigzag bands the mat is
''pmg''; with the details but without the distinction between brown and black it is
''pgg''.
Ignoring the wavy borders of the tiles, the pavement is
''pgg''.
Group ''cm'' (*×)
* Orbifold signature:
*×
* Coxeter notation:
+,2+,∞">infin;+,2+,∞or
+,∞+">infin;,2+,∞+* Lattice: rhombic
* Point group: D
1
* The group ''cm'' contains no rotations. It has reflection axes, all parallel. There is at least one glide reflection whose axis is ''not'' a reflection axis; it is halfway between two adjacent parallel reflection axes.
*This group applies for symmetrically staggered rows (i.e. there is a shift per row of half the translation distance inside the rows) of identical objects, which have a symmetry axis perpendicular to the rows.
;Examples of group ''cm''
Image:WallpaperCM.GIF, Computer generated
Image:Wallpaper_group-cm-1.jpg, Dress of Amun
Amun (; also ''Amon'', ''Ammon'', ''Amen''; egy, jmn, reconstructed as ( Old Egyptian and early Middle Egyptian) → (later Middle Egyptian) → ( Late Egyptian), cop, Ⲁⲙⲟⲩⲛ, Amoun) romanized: ʾmn) was a major ancient Egypt ...
, from Abu Simbel
Abu Simbel is a historic site comprising two massive rock-cut temples in the village of Abu Simbel ( ar, أبو سمبل), Aswan Governorate, Upper Egypt, near the border with Sudan. It is situated on the western bank of Lake Nasser, about ...
, Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...
Image:Wallpaper_group-cm-2.jpg, Dado from Biban el Moluk, Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...
Image:Wallpaper_group-cm-3.jpg, Bronze
Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids suc ...
vessel in Nimroud
Nimrud (; syr, ܢܢܡܪܕ ar, النمرود) is an ancient Assyrian city located in Iraq, south of the city of Mosul, and south of the village of Selamiyah ( ar, السلامية), in the Nineveh Plains in Upper Mesopotamia. It was a majo ...
, Assyria
Assyria ( Neo-Assyrian cuneiform: , romanized: ''māt Aššur''; syc, ܐܬܘܪ, ʾāthor) was a major ancient Mesopotamian civilization which existed as a city-state at times controlling regional territories in the indigenous lands of the A ...
Image:Wallpaper_group-cm-4.jpg, Spandrils of arch
An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it.
Arches may be synonymous with vau ...
es, the Alhambra, Spain
, image_flag = Bandera de España.svg
, image_coat = Escudo de España (mazonado).svg
, national_motto = '' Plus ultra'' (Latin)(English: "Further Beyond")
, national_anthem = (English: "Royal March")
, ...
Image:Wallpaper_group-cm-5.jpg, Soffitt of arch, the Alhambra, Spain
, image_flag = Bandera de España.svg
, image_coat = Escudo de España (mazonado).svg
, national_motto = '' Plus ultra'' (Latin)(English: "Further Beyond")
, national_anthem = (English: "Royal March")
, ...
Image:Wallpaper_group-cm-6.jpg, Persian tapestry
Tapestry is a form of textile art, traditionally woven by hand on a loom. Tapestry is weft-faced weaving, in which all the warp threads are hidden in the completed work, unlike most woven textiles, where both the warp and the weft threads ma ...
Image:Wallpaper_group-cm-7.jpg, India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
n metalwork at the Great Exhibition in 1851
Image:Wallpaper_group-pm-2.jpg, Dress of a figure in a tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
at Biban el Moluk, Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...
Group ''pmm'' (*2222)
* Orbifold signature:
*2222
* Coxeter notation (rectangular):
infin;,2,∞or
infin;�
infin;* Coxeter notation (square):
+,4">,1+,4or
+,4,4,1+">+,4,4,1+* Lattice: rectangular
* Point group: D
2
* The group ''pmm'' has reflections in two perpendicular directions, and four rotation centres of order two (180°) located at the intersections of the reflection axes.
;Examples of group ''pmm''
Image:Wallpaper_group-pmm-1.jpg, 2D image of lattice fence, U.S. (in 3D there is additional symmetry)
Image:Wallpaper_group-pmm-2.jpg, Mummy case stored in The Louvre
The Louvre ( ), or the Louvre Museum ( ), is the world's most-visited museum, and an historic landmark in Paris, France. It is the home of some of the best-known works of art, including the '' Mona Lisa'' and the ''Venus de Milo''. A centra ...
Image:Wallpaper_group-pmm-4.jpg, Mummy case stored in The Louvre
The Louvre ( ), or the Louvre Museum ( ), is the world's most-visited museum, and an historic landmark in Paris, France. It is the home of some of the best-known works of art, including the '' Mona Lisa'' and the ''Venus de Milo''. A centra ...
. Would be type ''p''4''m'' except for the mismatched coloring
Group ''pmg'' (22*)
* Orbifold signature:
22*
* Coxeter notation:
+,∞">∞,2)+,∞or
+">infin;,(2,∞)+* Lattice: rectangular
* Point group: D
2
* The group ''pmg'' has two rotation centres of order two (180°), and reflections in only one direction. It has glide reflections whose axes are perpendicular to the reflection axes. The centres of rotation all lie on glide reflection axes.
;Examples of group ''pmg''
Image:WallpaperPMG.GIF, Computer generated
Image:Wallpaper_group-pmg-1.jpg, Cloth, Sandwich Islands (Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
)
Image:Wallpaper_group-pmg-2.jpg, Ceiling of Egyptian tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
Image:Wallpaper_group-pmg-3.jpg, Floor tiling in Prague
Prague ( ; cs, Praha ; german: Prag, ; la, Praga) is the capital and largest city in the Czech Republic, and the historical capital of Bohemia. On the Vltava river, Prague is home to about 1.3 million people. The city has a temperate ...
, the Czech Republic
The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...
Image:Wallpaper_group-pmg-4.jpg, Bowl from Kerma
Kerma was the capital city of the Kerma culture, which was located in present-day Sudan at least 5,500 years ago. Kerma is one of the largest archaeological sites in ancient Nubia. It has produced decades of extensive excavations and research, ...
Image:2-d pentagon packing.svg, Pentagon packing
Group ''pgg'' (22×)
* Orbifold signature:
22×
* Coxeter notation (rectangular):
+,(∞,2)+)">(∞,2)+,(∞,2)+)* Coxeter notation (square):
+,4+">+,4+* Lattice: rectangular
* Point group: D
2
* The group ''pgg'' contains two rotation centres of order two (180°), and glide reflections in two perpendicular directions. The centres of rotation are not located on the glide reflection axes. There are no reflections.
;Examples of group ''pgg''
Image:WallpaperPGG.GIF, Computer generated
Image:Wallpaper_group-pgg-1.jpg, Bronze
Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids suc ...
vessel in Nimroud
Nimrud (; syr, ܢܢܡܪܕ ar, النمرود) is an ancient Assyrian city located in Iraq, south of the city of Mosul, and south of the village of Selamiyah ( ar, السلامية), in the Nineveh Plains in Upper Mesopotamia. It was a majo ...
, Assyria
Assyria ( Neo-Assyrian cuneiform: , romanized: ''māt Aššur''; syc, ܐܬܘܪ, ʾāthor) was a major ancient Mesopotamian civilization which existed as a city-state at times controlling regional territories in the indigenous lands of the A ...
Image:Wallpaper_group-pgg-2.jpg, Pavement in Budapest
Budapest (, ; ) is the capital and most populous city of Hungary. It is the ninth-largest city in the European Union by population within city limits and the second-largest city on the Danube river; the city has an estimated population o ...
, Hungary
Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Cr ...
Group ''cmm'' (2*22)
* Orbifold signature:
2*22
* Coxeter notation (rhombic):
+,∞">infin;,2+,∞* Coxeter notation (square):
+)">4,4,2+)* Lattice: rhombic
* Point group: D
2
* The group ''cmm'' has reflections in two perpendicular directions, and a rotation of order two (180°) whose centre is ''not'' on a reflection axis. It also has two rotations whose centres ''are'' on a reflection axis.
*This group is frequently seen in everyday life, since the most common arrangement of
bricks in a brick building (
running bond) utilises this group (see example below).
The rotational symmetry of order 2 with centres of rotation at the centres of the sides of the rhombus is a consequence of the other properties.
The pattern corresponds to each of the following:
*symmetrically staggered rows of identical doubly symmetric objects
*a checkerboard pattern of two alternating rectangular tiles, of which each, by itself, is doubly symmetric
*a checkerboard pattern of alternatingly a 2-fold rotationally symmetric rectangular tile and its mirror image
;Examples of group ''cmm''
Image:WallpaperCMM.GIF, Computer generated
File:1-uniform_n8.svg, Elongated triangular tiling
Image:Wallpaper_group-cmm-1.jpg, Suburban brick wall using running bond arrangement, U.S.
Image:Wallpaper_group-cmm-2.jpg, Ceiling of Egyptian tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
. Ignoring colors, this would be ''p''4''g''
Image:Wallpaper_group-cmm-3.jpg, Egyptian
Image:Wallpaper_group-cmm-4.jpg, Persian tapestry
Tapestry is a form of textile art, traditionally woven by hand on a loom. Tapestry is weft-faced weaving, in which all the warp threads are hidden in the completed work, unlike most woven textiles, where both the warp and the weft threads ma ...
Image:Wallpaper_group-cmm-5.jpg, Egyptian tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
Image:Wallpaper_group-cmm-6.jpg, Turkish dish
Image:2-d dense packing r1.svg, A compact packing of two sizes of circle
Image:2-d dense packing r3.svg, Another compact packing of two sizes of circle
Image:2-d dense packing r7.svg, Another compact packing of two sizes of circle
Group ''p''4 (442)
* Orbifold signature:
442
* Coxeter notation:
,4sup>+
* Lattice: square
* Point group: C
4
* The group ''p''4 has two rotation centres of order four (90°), and one rotation centre of order two (180°). It has no reflections or glide reflections.
;Examples of group ''p''4
A ''p''4 pattern can be looked upon as a repetition in rows and columns of equal square tiles with 4-fold rotational symmetry. Also it can be looked upon as a
checkerboard
A checkerboard (American English) or chequerboard (British English; see spelling differences) is a board of checkered pattern on which checkers (also known as English draughts) is played. Most commonly, it consists of 64 squares (8×8) of altern ...
pattern of two such tiles, a factor smaller and rotated 45°.
Image:WallpaperP4.GIF, Computer generated
Image:Wallpaper_group-p4-1.jpg, Ceiling of Egyptian tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
; ignoring colors this is ''p''4, otherwise ''p''2
Image:Wallpaper_group-p4-2.jpg, Ceiling of Egyptian tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
Image:A_wallpaper_pattern_Overlaid_patterns.svg, Overlaid patterns
Image:Wallpaper_group-p4-3.jpg, Frieze, the Alhambra, Spain
, image_flag = Bandera de España.svg
, image_coat = Escudo de España (mazonado).svg
, national_motto = '' Plus ultra'' (Latin)(English: "Further Beyond")
, national_anthem = (English: "Royal March")
, ...
. Requires close inspection to see why there are no reflections
Image:Wallpaper_group-p4-4.jpg, Viennese cane
Image:Wallpaper_group-p4-5.jpg, Renaissance earthenware
File:A tri-colored Pythagorean tiling View 4.svg, Pythagorean tiling
File:Lizard p4 p4.png, Generated from a photograph
Group ''p''4''m'' (*442)
* Orbifold signature:
*442
* Coxeter notation:
,4* Lattice: square
* Point group: D
4
* The group ''p''4''m'' has two rotation centres of order four (90°), and reflections in four distinct directions (horizontal, vertical, and diagonals). It has additional glide reflections whose axes are not reflection axes; rotations of order two (180°) are centred at the intersection of the glide reflection axes. All rotation centres lie on reflection axes.
This corresponds to a straightforward grid of rows and columns of equal squares with the four reflection axes. Also it corresponds to a
checkerboard
A checkerboard (American English) or chequerboard (British English; see spelling differences) is a board of checkered pattern on which checkers (also known as English draughts) is played. Most commonly, it consists of 64 squares (8×8) of altern ...
pattern of two of such squares.
;Examples of group ''p''4''m''
Examples displayed with the smallest translations horizontal and vertical (like in the diagram):
Image:WallpaperP4M.GIF, Computer generated
Image:1-uniform_n5.svg, Square tiling
Image:Tile V488.svg, Tetrakis square tiling; ignoring colors, this is ''p''4''m'', otherwise ''c''2''m''
Image:Tile 488.svg, Truncated square tiling (ignoring color also, with smaller translations)
Image:Wallpaper_group-p4m-1.jpg, Ornamental painting, Nineveh
Nineveh (; akk, ; Biblical Hebrew: '; ar, نَيْنَوَىٰ '; syr, ܢܝܼܢܘܹܐ, Nīnwē) was an ancient Assyrian city of Upper Mesopotamia, located in the modern-day city of Mosul in northern Iraq. It is located on the eastern ba ...
, Assyria
Assyria ( Neo-Assyrian cuneiform: , romanized: ''māt Aššur''; syc, ܐܬܘܪ, ʾāthor) was a major ancient Mesopotamian civilization which existed as a city-state at times controlling regional territories in the indigenous lands of the A ...
Image:Wallpaper_group-p4m-3.jpg, Storm drain
A storm drain, storm sewer (United Kingdom, U.S. and Canada), surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from impervious surfa ...
, U.S.
Image:Wallpaper_group-p4m-5.jpg, Egyptian mummy case
Image:Wallpaper_group-p4m-6.jpg, Persian glazed tile
Image:2-d dense packing r4.svg, Compact packing of two sizes of circle
Examples displayed with the smallest translations diagonal:
Image:Tile 4,4.svg, checkerboard
Image:Wallpaper_group-p4m-2.jpg, Cloth, Otaheite ( Tahiti)
Image:Wallpaper_group-p4m-4.jpg, Egyptian tomb
A tomb ( grc-gre, τύμβος ''tumbos'') is a repository for the remains of the dead. It is generally any structurally enclosed interment space or burial chamber, of varying sizes. Placing a corpse into a tomb can be called ''immureme ...
Image:Wallpaper_group-p4m-7.jpg, Cathedral of Bourges
Image:Wallpaper_group-p4m-8.jpg, Dish from Turkey
Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula ...
, Ottoman period
Group ''p''4''g'' (4*2)
* Orbifold signature:
4*2
* Coxeter notation:
+,4">+,4* Lattice: square
* Point group: D
4
* The group ''p''4''g'' has two centres of rotation of order four (90°), which are each other's mirror image, but it has reflections in only two directions, which are perpendicular. There are rotations of order two (180°) whose centres are located at the intersections of reflection axes. It has glide reflections axes parallel to the reflection axes, in between them, and also at an angle of 45° with these.
A ''p''4''g'' pattern can be looked upon as a
checkerboard
A checkerboard (American English) or chequerboard (British English; see spelling differences) is a board of checkered pattern on which checkers (also known as English draughts) is played. Most commonly, it consists of 64 squares (8×8) of altern ...
pattern of copies of a square tile with 4-fold rotational symmetry, and its mirror image. Alternatively it can be looked upon (by shifting half a tile) as a checkerboard pattern of copies of a horizontally and vertically symmetric tile and its 90° rotated version. Note that neither applies for a plain checkerboard pattern of black and white tiles, this is group
''p''4''m'' (with diagonal translation cells).
;Examples of group ''p''4''g''
Image:Wallpaper_group-p4g-1.jpg, Bathroom linoleum, U.S.
Image:Wallpaper_group-p4g-2.jpg, Painted porcelain
Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises main ...
, China
Image:Wallpaper_group-p4g-3.jpg, Fly screen, U.S.
Image:Wallpaper_group-p4g-4.jpg, Painting, China
File:Uniform tiling 44-h01.png, one of the colorings of the snub square tiling (see also at ''pg'')
Group ''p''3 (333)
* Orbifold signature:
333
* Coxeter notation:
3,3,3)sup>+ or
[3/sup>.html"_;"title=".html"_;"title="
[3">[3/sup>">.html"_;"title="[3">[3/sup>sup>+
*_Lattice:_hexagonal
*_Point_group:_C3
*_The_group_''p''3_has_three_different_rotation_centres_of_order_three_(120°),_but_no_reflections_or_glide_reflections.
Imagine_a_tessellation_
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_...
_of_the_plane_with_equilateral_triangles_of_equal_size,_with_the_sides_corresponding_to_the_smallest_translations._Then_half_of_the_triangles_are_in_one_orientation,_and_the_other_half_upside_down._This_wallpaper_group_corresponds_to_the_case_that_all_triangles_of_the_same_orientation_are_equal,_while_both_types_have_rotational_symmetry_of_order_three,_but_the_two_are_not_equal,_not_each_other's_mirror_image,_and_not_both_symmetric_(if_the_two_are_equal_it_is_''p''6,_if_they_are_each_other's_mirror_image_it_is_''p''31''m'',_if_they_are_both_symmetric_it_is_''p''3''m''1;_if_two_of_the_three_apply_then_the_third_also,_and_it_is_''p''6''m'')._For_a_given_image,_three_of_these_tessellations_are_possible,_each_with_rotation_centres_as_vertices,_i.e._for_any_tessellation_two_shifts_are_possible._In_terms_of_the_image:_the_vertices_can_be_the_red,_the_blue_or_the_green_triangles.
Equivalently,_imagine_a_tessellation_of_the_plane_with_regular_hexagons,_with_sides_equal_to_the_smallest_translation_distance_divided_by_._Then_this_wallpaper_group_corresponds_to_the_case_that_all_hexagons_are_equal_(and_in_the_same_orientation)_and_have_rotational_symmetry_of_order_three,_while_they_have_no_mirror_image_symmetry_(if_they_have_rotational_symmetry_of_order_six_it_is_''p''6,_if_they_are_symmetric_with_respect_to_the_main_diagonals_it_is_''p''31''m'',_if_they_are_symmetric_with_respect_to_lines_perpendicular_to_the_sides_it_is_''p''3''m''1;_if_two_of_the_three_apply_then_the_third_also,_it_is_''p''6''m'')._For_a_given_image,_three_of_these_tessellations_are_possible,_each_with_one_third_of_the_rotation_centres_as_centres_of_the_hexagons._In_terms_of_the_image:_the_centres_of_the_hexagons_can_be_the_red,_the_blue_or_the_green_triangles.
;Examples_of_group_''p''3