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In layman's terms, the genus is the number of "holes" an object has ("holes" interpreted in the sense of doughnut holes; a hollow sphere would be considered as having zero holes in this sense). [3] A torus has 1 such hole, while a sphere has 0. The green surface pictured above has 2 holes of the relevant sort. For instance:
A word equation is a formal equality:= = between a pair of words and , each over an alphabet comprising both constants (c.f. ) and unknowns (c.f. ). [1] An assignment of constant words to the unknowns of is said to solve if it maps both sides of to identical words.
Wheel graphs W 2n+1, for n ≥ 2, are not word-representable and W 5 is the minimum (by the number of vertices) non-word-representable graph. Taking any non-comparability graph and adding an apex (a vertex connected to any other vertex), we obtain a non-word-representable graph, which then can produce infinitely many non-word-representable ...
To formally define this relation, we define the following commutative groups: [2]: 6:00 C 0 is the free abelian group generated by the set of vertices {x,y,z}. Each element of C 0 is called a 0-dimensional chain. C 1 is the free abelian group generated by the set of directed edges {a,b,c,d}. Each element of C 1 is called a 1-dimensional chain.
For a torus, the first Betti number is b 1 = 2 , which can be intuitively thought of as the number of circular "holes" Informally, the kth Betti number refers to the number of k-dimensional holes on a topological surface. A "k-dimensional hole" is a k-dimensional cycle that is not a boundary of a (k+1)-dimensional object.
Alternatively, a graph is diamond-free if and only if every pair of maximal cliques in the graph shares at most one vertex. The family of graphs in which each connected component is a cactus graph is downwardly closed under graph minor operations. This graph family may be characterized by a single forbidden minor. This minor is the diamond ...
In it, geometrical shapes can be made, as well as expressions from the normal graphing calculator, with extra features. [8] In September 2023, Desmos released a beta for a 3D calculator, which added features on top of the 2D calculator, including cross products, partial derivatives and double-variable parametric equations.
This is a graph with vertex set the pants decompositions of , and two vertices are joined if they are related by an elementary move, which is one of the two following operations: take a curve α {\displaystyle \alpha } in the decomposition in a one-holed torus and replace it by a curve in the torus intersecting it only once,