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2. Outerplanar graph - Wikipedia

   en.wikipedia.org/wiki/Outerplanar_graph

   An outer-1-planar graph, analogously to 1-planar graphs can be drawn in a disk, with the vertices on the boundary of the disk, and with at most one crossing per edge. Every maximal outerplanar graph is a chordal graph. Every maximal outerplanar graph is the visibility graph of a simple polygon. [17]

3. k-outerplanar graph - Wikipedia

   en.wikipedia.org/wiki/K-Outerplanar_graph

   An outerplanar graph (or 1-outerplanar graph) has all of its vertices on the unbounded (outside) face of the graph. A 2-outerplanar graph is a planar graph with the property that, when the vertices on the unbounded face are removed, the remaining vertices all lie on the newly formed unbounded face. And so on.

4. Wagner's theorem - Wikipedia

   en.wikipedia.org/wiki/Wagner's_theorem

   Proof without words that a hypercube graph is non-planar using Kuratowski's or Wagner's theorems and finding either K 5 (top) or K 3,3 (bottom) subgraphs. Wagner published both theorems in 1937, [1] subsequent to the 1930 publication of Kuratowski's theorem, [2] 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 ...

5. Complete graph - Wikipedia

   en.wikipedia.org/wiki/Complete_graph

   Geometrically K 3 forms the edge set of a triangle, K 4 a tetrahedron, etc. The Császár polyhedron, a nonconvex polyhedron with the topology of a torus, has the complete graph K 7 as its skeleton. [15] Every neighborly polytope in four or more dimensions also has a complete skeleton. K 1 through K 4 are all planar graphs.

6. Kuratowski's theorem - Wikipedia

   en.wikipedia.org/wiki/Kuratowski's_theorem

   Proof without words that a hypercube graph is non-planar using Kuratowski's or Wagner's theorems and finding either K 5 (top) or K 3,3 (bottom) subgraphs. If is a graph that contains a subgraph that is a subdivision of or ,, then is known as a Kuratowski subgraph of . [1]

7. Graph power - Wikipedia

   en.wikipedia.org/wiki/Graph_power

   K 4 as the half-square of a cube graph. The half-square of a bipartite graph G is the subgraph of G 2 induced by one side of the bipartition of G. Map graphs are the half-squares of planar graphs, [18] and halved cube graphs are the half-squares of hypercube graphs. [19] Leaf powers are the subgraphs of powers of trees induced by the leaves of ...

8. Robertson–Seymour theorem - Wikipedia

   en.wikipedia.org/wiki/Robertson–Seymour_theorem

   Wagner's theorem states that a graph is planar if and only if it has neither K 5 nor K 3,3 as a minor. In other words, the set {K 5, K 3,3} is an obstruction set for the set of all planar graphs, and in fact the unique minimal obstruction set. A similar theorem states that K 4 and K 2,3 are the forbidden minors for the set of outerplanar graphs.

9. Complete bipartite graph - Wikipedia

   en.wikipedia.org/wiki/Complete_bipartite_graph

   A planar graph cannot contain K 3,3 as a minor; an outerplanar graph cannot contain K 3,2 as a minor (These are not sufficient conditions for planarity and outerplanarity, but necessary). Conversely, every nonplanar graph contains either K 3,3 or the complete graph K 5 as a minor; this is Wagner's theorem. [9] Every complete bipartite graph.