semisäännölliset

Semisäännölliset is a Finnish term that translates to "semiregular" in English. It is most commonly used in the context of geometry and describes objects that exhibit a degree of regularity but not complete regularity. This can apply to polygons, polyhedra, or tilings.

In geometry, a regular polygon has all sides equal and all angles equal. A semisymmetrical polygon, on the other hand, might have equal sides but unequal angles, or equal angles but unequal sides, or some combination of these properties. For example, a rectangle is a semisymmetrical quadrilateral as it has four right angles but not necessarily equal sides. A rhombus is also semisymmetrical because it has equal sides but not necessarily equal angles.

The concept extends to three dimensions. A regular polyhedron, such as a cube or a tetrahedron, has all faces as congruent regular polygons and the same number of faces meeting at each vertex. A semisymmetrical polyhedron might have faces that are all congruent but not regular polygons, or faces that are regular polygons but not all congruent. An example of a semisymmetrical polyhedron is a prism with a regular polygon as its base and rectangular sides.

Semisymmetrical tilings are arrangements of shapes that cover a plane without gaps or overlaps. A regular tiling uses only one type of regular polygon. A semisymmetrical tiling might use multiple types of regular polygons, or shapes that are not regular polygons, but still exhibits some repeating pattern or symmetry. The term implies a structure that is more structured than completely random but less structured than perfectly regular.