# Context help

### The tiling

The tiling is a regular filling of the plane, done with a single figure. The basic figure is the tile: The fundamental set of tiles is a group of several tiles which allows to do the tiling in 2 directions of translations: ### Fundamental set of tiles

The fundamental set of tiles is a group of several tiles which allows to do the tiling in 2 directions of translations. ### Tile

The tile is the basic element for a tiling As a tile is in contact with another, each part of its contour appears twice. ### Group of displacement

Each type of tiling is associated to a group of displacement of the plane. This group is made of the displacement allowing to go from one tile to another.

The displacements are:

The groups associated to a different type of tiling are always the results of a finite number of displacements, within which are 2 translations.

### Translations In a translation, you displace the figure without turning it over or upside down.
The translation is represented by an arrow called vector.
The 2 translations associated to each tiling allow to go from one fundamental set of tiles to another. ### Rotations In a rotation, the figure turns around a point called center.
It is also necessary to know the angle of rotation.
The rotations associated to a tiling always have their angles being equal to:

• 1/6 of rotation and multiple angles (2/6=1/3, 3/6=1/2, 4/6=2/3 and 5/6) • 1/4 of rotation and multiple angles (2/4=1/2 and 3/4) • 1/3 of rotation and multiple angles (2/3) • 1/2 of rotation (these are central symmetries) The centers of rotation are always on the contour of the tile: ### Central symmetries A central symmetry is a rotation the angle of which is a 1/2 turn.

### Axial symmetries In an axial symmetry, the figure is turned around an axis.
When a tiling has an axis of symmetry, a part of the contour of the tile is along this axis and cannot be distorted. The tilings with several directions of angles of symmetry, often have a fixed contour: ### Glide reflections You can get a glide reflection if you compose an axial symmetry with a translation the vector of which is parallel to the axis of symmetry.

### Group

A group is a set (let us call it G) with a law of internal composition (if x and y are parts of G , x¤y too) associative (x ¤ y) ¤ z = x ¤ (y ¤ z),We can then write x¤y¤z) as a neutral element exists (e is the neutral element if, for each x, we’ve got x ¤ e = e ¤ x = x) and if each element has an inverse (reciprocal) (for each x , y exists as x ¤ y = y ¤ x = e).

Examples: * the integers (positive or negative) form a group for addition (the neutral element is zero and the opposite (additive inverse) of 5 is -5 * however, positive integers , don’t form a group for addition * the displacements of the plane form a group for composition.

### Composition

The composition of two displacements of the plane consists in doing two displacements one after the other.

Example:

• The composition of two translations is a translation: • The composition of a translation and a rotation is a rotation: • The composition of two axial symmetries is a translation or a rotation:  # The 17 types of tilings

### (asymmetric parallelogramic) The fundamental set of tiles is made of a single tile: The group of displacement is generated by only two translations.

The contour of the tile has got 2 parts: ### (symmetric parallelogramic) The fundamental set of tiles is made of 2 tiles: The group of displacement is generated by The contour of the tile has got 4 parts: ### (hexagonal 3-rotative) The fundamental set of tiles is made of 3 tiles and both the vectors form an equilateral triangle: The group of displacement is generated by The contour of the tile has got 3 parts: ### (square 4-rotative) The fundamental set of tiles is made of 4 tiles, and both the vectors form a half square: The group of displacement is generated by The contour of the tile has got 3 parts: ### (hexagonal 6-rotative) The fundamental set of tiles is made of 6 tiles, and both the vectors form an equilateral triangle: The group of displacement is generated by The contour of the tile has got 3 parts: ### (gliding rectangular) The fundamental set of tiles is made of 2 tiles, and both the vectors form a half rectangle: The group of displacement is generated by The contour of the tile has got 3 parts: ### (bi-gliding rectangular) The fundamental set of tiles is made of 4 tiles, and both the vectors form a half rectangle: The group of displacement is generated by The contour of the tile has got 4 parts: ### (mono-symmetric rectangular) The fundamental set of tiles is made of 2 tiles, and both the vectors form a half rectangle: The group of displacement is generated by The contour of the tile has got 2 parts: ### (mono-symmetric rhombic) The fundamental set of tiles is made of 2 tiles, and both the vectors form an isosceles triangle: The group of displacement is generated by The contour of the tile has got 3 parts: ### (symmetric gliding

rectangular) The fundamental set of tiles is made of 4 tiles, and both the vectors form a half rectangle: The group of displacement is generated by The contour of the tile has got 3 parts: ### (bi-symmetric rectangular) The fundamental set of tiles is made of 4 tiles, and both the vectors form a half rectangle: The group of displacement is generated by The contour of the tile is a rectangle.

### (bi-symmetric rhombic) The fundamental set of tiles is made of 4 tiles, and both the vectors form an isosceles triangle: The group of displacement is generated by The contour of the tile has got 3 parts: ### (gliding 4-rotative square) The fundamental set of tiles is made of 8 tiles, and both the vectors form a half square: The group of displacement is generated by The contour of the tile has got 2 parts: ### (tri-symmetric hexagonal) The fundamental set of tiles is made of 6 tiles, and both the vectors form an equilateral triangle: The group of displacement is generated by The contour of the tile is an equilateral triangle.

### (symmetric 3-rotative hexagonal) The fundamental set of tiles is made of 6 tiles, and both the vectors form an equilateral triangle: The group of displacement is generated by The contour of the tile has got 2 parts: ### (totally symmetric square) The fundamental set of tiles is made of 8 tiles, and both the vectors form a half square: The group of displacement is generated by The contour of the tile is a right and isosceles triangle (half square).

### (totally symmetric hexagonal) The fundamental set of tiles is made of 12 tiles, and both the vectors form an equilateral triangle: The group of displacement is generated by The contour of the tile is a right triangle, the angles are 30°, 60° and 90°.