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In hyperbolic geometry, the "law of cosines" is a pair of theorems relating the sides and angles of triangles on a hyperbolic plane, analogous to the planar law of cosines from plane trigonometry, or the spherical law of cosines in spherical trigonometry. [1] It can also be related to the relativistic velocity addition formula. [2] [3]
Let f : X → B be a holomorphic submersive morphism. For a point b of B, we denote the fiber of f over b by X b.Fix a point 0 in B.Ehresmann's theorem guarantees that there is a small open neighborhood U around 0 in which f becomes a fiber bundle.
For every combinatorial cell complex, one defines the Euler characteristic as the number of 0-cells, minus the number of 1-cells, plus the number of 2-cells, etc., if this alternating sum is finite. In particular, the Euler characteristic of a finite set is simply its cardinality, and the Euler characteristic of a graph is the number of ...
[2] 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]
[1] [2] A Euclidean graph is uniformly discrete if there is a minimal distance between any two vertices. Periodic graphs are closely related to tessellations of space (or honeycombs) and the geometry of their symmetry groups, hence to geometric group theory, as well as to discrete geometry and the theory of polytopes, and similar areas.
A tiling that has no periods is non-periodic. A set of prototiles is said to be aperiodic if all of its tilings are non-periodic, and in this case its tilings are also called aperiodic tilings. [5] Penrose tilings are among the simplest known examples of aperiodic tilings of the plane by finite sets of prototiles. [3]
If the points are sequentially numbered and located at positions r 1, r 2, r 3, etc. then bond vectors are defined by u 1 = r 2 − r 1, u 2 = r 3 − r 2, and u i = r i+1 − r i, more generally. [2] This is the case for kinematic chains or amino acids in a protein structure. In these cases, one is often interested in the half-planes defined ...
For example: 3 6; 3 6; 3 4.6, tells us there are 3 vertices with 2 different vertex types, so this tiling would be classed as a ‘3-uniform (2-vertex types)’ tiling. Broken down, 3 6 ; 3 6 (both of different transitivity class), or (3 6 ) 2 , tells us that there are 2 vertices (denoted by the superscript 2), each with 6 equilateral 3-sided ...