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9 votes
3 answers
470 views

Is it possible that every edge in a 1-planar drawing with minimum number of crossings is crossed?

A graph is 1-planar is it has drawing in the plane so that each edge is crossed at most once. Here we also assume the drawing satisfies (1) no edge is self-crossed; (2) no two adjacent edges are ...
W. Paul Liu's user avatar
4 votes
0 answers
131 views

What is the crossing number of dodecahedron with a copy of $K_5$ inside each face

Suppose we are given a regular dodecahedron. Then we add five crossed edges inside each of its faces (actually, inside each face it is a copy of $K_5$). It is clear that this drawing has 60 crossings. ...
Xin Zhang's user avatar
  • 1,190
5 votes
1 answer
263 views

What is the crossing number of cube with a pair of crossing edges inside each face

Suppose we are given a cube and we add a pair of crossing edges inside each of its faces. It is clear that this drawing has 6 crossings. My question is whether such a graph has crossing number 6? How ...
Xin Zhang's user avatar
  • 1,190
3 votes
1 answer
200 views

Looking for examples showing that the crossing number may not be realized by the drawings with local crossing number

The crossing number $cr(G)$ of a graph $G$ is the lowest number of edge crossings of a plane drawing of the graph $G$. The local crossing number of a drawing of a graph is the largest number of ...
Xin Zhang's user avatar
  • 1,190
7 votes
2 answers
252 views

There is a 3-connected 5-regular simple $n$-vertex planar graph iff $n$ satisfies....?

Is there any characterization on the set of integers $n$ such that there is a 3-connected 5-regular simple $n$-vertex planar graph?
Xin Zhang's user avatar
  • 1,190
6 votes
2 answers
293 views

Is there any maximal 1-planar or 2-planar graph that is not 3-connected

A graph is $k$-planar if it can be drawn in the plane so that each edge is crossed at most $k$ times. A $k$-planar graph $G$ is maximal if $G+uv$ is not $k$-planar for any non-adjacent vertices $u,v\...
Xin Zhang's user avatar
  • 1,190
1 vote
1 answer
228 views

Counting edges in embeddable CW-complexes in R^3

Using Euler's formula ($V-E+F = 2$ where $V$, $E$ and $F$ are the number of vertices, edges and faces), we can easily count the number of edges in maximal graphs that are embeddable in plane: 3n-6. I ...
Hooman's user avatar
  • 415