Примеры использования Is planar if and only на Английском языке и их переводы на Русский язык
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The Hasse diagram of a lattice is planar if and only if  its order dimension is at most two.
Another result also sometimes known as Wagner's theorem states that a four-connected graph is planar if and only if  it has no K5 minor.
Wagner's theorem states that a graph is planar if and only if  it has neither K5 nor K3,3 as a minor.
In graph theory, the crossing number cr(G) of a graph G is  the lowest number of edge crossings of a plane drawing of the graph G. For instance,a graph is planar if and only if  its crossing number is zero.
Schnyder's theorem states that a graph G is planar if and only if  the order dimension of P(G) is at most three.
It states that a graph G is planar if and only if  its graphic matroid is also cographic that is, it is the dual matroid of another graphic matroid.
Correspondingly, the Kelmans-Seymour conjecture states that a 5-connected graph is planar if and only if  it does not have K5 as a topological minor.
Wagner's theorem that a graph is planar if and only if  it does not contain a minor(subgraph of a contraction) that is isomorphic to K5 or K3,3.
Wagner published both theorems in 1937, subsequent to the 1930 publication of Kuratowski's theorem,according to which a graph is planar if and only if  it does not contain as a subgraph a subdivision of one of the same two forbidden graphs K5 and K3,3.
These include Kuratowski's theorem that a graph is planar if and only if  it does not contain a subgraph that is a subdivision of K5(the complete graph on five vertices) or K3,3 the utility graph, a complete bipartite graph on six vertices, three of which connect to each of the other three.
Mac Lane's planarity criterion uses this idea to characterize the planar  graphs in terms of the cycle bases: a finite undirected graph is planar if and only if  it has a sparse cycle basis or 2-basis, a basis in which each edge of the graph participates in at most two basis cycles.
An equivalent form of Whitney 's criterion is  that a graph G is planar if and only if  it has a dual graph whose graphic matroid is dual to the graphic matroid of G. A graph whose graphic matroid is dual to the graphic matroid of G is known as an algebraic dual of G. This, Whitney 's planarity criterion can be expressed succinctly as: a graph is planar if and only if  it has an algebraic dual.
One of these two families is  formed by replacing the nodes of a cycle by fragments A and B, with at least two of the fragments being  of type A; a graph of this type is planar if and only if  it does not contain any fragments of type B. The other family is formed by replacing the nodes of a path by fragments of type B and C; all such graphs are planar. .
It states that a finite undirected graph is planar if and only if  the cycle space of the graph(taken modulo 2) has a cycle basis in which each edge of the graph participates in at most two basis vectors.
As they showed, when the base graph is  biconnected,a graph constructed in this way is planar if and only if  its base graph is outerplanar and the matching forms a dihedral permutation of its outer cycle.
Kuratowski's theorem states that a finite graph is planar if and only if  it contains no subgraph homeomorphic to K5(complete graph on five vertices) or K3,3 complete bipartite graph on two partitions of size three.
The theory of graph minors began with Wagner's theorem that a graph is planar if and only if  its minors include neither the complete graph K5 nor the complete bipartite graph K3,3.
He uses a slightly different formulation of the planarity criterion,according to which a graph is planar if and only if  it has a set of(not necessarily simple) cycles covering every edge exactly twice, such that the only nontrivial relation among these cycles in C(G) is that their sum be zero.
Other planarity criteria, that characterize planar  graphs mathematically but are  less central to planarity testing algorithms,include Whitney 's planarity criterion that a graph is planar if and only if  its graphic matroid is also cographic, Mac Lane 's planarity criterion characterizing planar graphs by the bases of their cycle spaces, Schnyder 's theorem characterizing planar graphs by the order dimension of an associated partial order, and Colin de Verdière 's planarity criterion using spectral graph theory.
A planar graph is outerplanar if and only if each of its biconnected components is  outerplanar.
More precisely, the book thickness of a graph G is  at most two if and only if G is a subgraph of a planar graph that has a Hamiltonian cycle.
In a maximal planar graph, the book thickness is two if and only if a Hamiltonian cycle exists.
A planar graph is outerplanar if and only if  its weak dual is  a forest, and  it is  Halin if and only if  its weak dual is  biconnected and  outerplanar.
A maximal planar graph is node-pancyclic if and only if  it has a Hamiltonian cycle:if  it is  not Hamiltonian, it is  certainly not pancyclic, and if  it is  Hamiltonian, then the interior of the Hamiltonian cycle forms a maximal outerplanar graph on the same nodes, to which the previous argument for maximal outerplanar graphs can be  applied.
In the case of three-dimensional polyhedra, this property and planarity may be used to exactly characterize the graphs of polyhedra: Steinitz's theorem states that G is  the skeleton of a three-dimensional polyhedron if and only if  G is a 3-vertex-connected planar graph.
A prototypical example of this phenomenon is  Kuratowski's theorem,which states that a graph is planar(can be  drawn without crossings in the plane) if and only if it does not contain either of two forbidden graphs, the complete graph K5 and  the complete bipartite graph K3,3.
In a maximal planar  graph, or more generally in every polyhedral graph,the peripheral cycles are  exactly the faces of a planar embedding of the graph, so a polyhedral graph is  strangulated if and only if  all the faces are triangles, or equivalently it is maximal planar. .
A graph is  k-vertex-connected, but not necessarily planar,  if and only if it has an embedding into(k -1)-dimensional space in which an arbitrary k-tuple of vertices are  placed at the vertices of a simplex and,  for each remaining vertex v, the convex hull of the neighbors of v is full-dimensional with v in its interior.
A directed acyclic graph G has an upward planar  drawing if and only if G is a subgraph of an st-planar graph.