# Quick Answer: Can A Non Planar Graph Be 4 Colors?

## Who Solved the four color map problem?

The four-colour problem was solved in 1977 by a group of mathematicians at the University of Illinois, directed by Kenneth Appel and Wolfgang Haken, after four years of unprecedented synthesis of computer search and theoretical reasoning..

## How was the four color theorem proved?

[1]. A computer-assisted proof of the four color theorem was proposed by Kenneth Appel and Wolfgang Haken in 1976. Their proof reduced the infinitude of possible maps to 1,936 reducible configurations (later reduced to 1,476) which had to be checked one by one by computer and took over a thousand hours [1].

## Is the 2 coloring problem in P or in NP?

Since graph 2-coloring is in P and it is not the trivial language (∅ or Σ∗), it is NP-complete if and only if P=NP.

## What is a K3 3 graph?

The graph K3,3 is non-planar. Proof: in K3,3 we have v = 6 and e = 9. If K3,3 were planar, from Euler’s formula we would have f = 5. On the other hand, each region is bounded by at least four edges, so 4f ≤ 2e, i.e., 20 ≤ 18, which is a contradiction.

## What is N colorable?

A graph is said to be k-colorable if it can be properly colored using k colors. … Conversely, if a graph is 2-colorable, then the vertices having same color can be taken as disjoint sets. Hence, we arrive at the following result: Theorem: A graph is bipartite if and only if it is 2-colorable.

## Why is the four color theorem important?

In addition to its inviting simplicity, the Four Color Theorem is famous for its inflection point in the history of math: it was the very first major theorem “proved” through brute-forcing scenarios with a computer. In today’s day-&-age that’s a rather historically-significant breakthrough.

## Why is coloring a graph necessary?

Actual colors have nothing at all to do with this, graph coloring is used to solve problems where you have a limited amount of resources or other restrictions. … Coloring here means attaching a “color” or a number to each vertice such that no two vertices with a connecting edge have the save value.

## Which of the following graph is not 3-colorable?

Almost all graphs with 2.522 n edges are not 3-colorable. Electronic Journal of Combinatorics, 6(1), R29.

## What is the chromatic number of each graph?

A graph coloring is an assignment of labels, called colors, to the vertices of a graph such that no two adjacent vertices share the same color. The chromatic number χ(G) of a graph G is the minimal number of colors for which such an assignment is possible.

## How do you know if a graph is three colorable?

Let x be a vertex in V (G) − (N[v] ∪ N2(v)). In any proper 3-coloring of G, if it exists, the vertex x either gets the same color as v or x receives a different color than v. Therefore it is enough to determine if any of the graphs G/xv and G ∪ xv are 3-colorable. Recall that by our hypothesis d(x) ≥ 8.

## Is 4 coloring NP complete?

Since 4-COLOR is in NP and NP-hard, we know it is NP-complete.

## What are the 5 colors on a map?

There are five different colors on a military map: Brown, Red, Blue, Black, and Green. Colors are used to make the map easier to read. Some maps add an additional color to make the map readable in the dark.

## Is every planar graph 3 colorable?

Every planar graph without adjacent 3-cycles and without 5-cycles is 3-colorable. (By intersecting (adjacent) triangles we mean those with a vertex (an edge) in common.)

## Can a non planar graph be colored with 4 colors?

3 Answers. Obviously not. A graph is bipartite if and only if it is 2-colorable, but not every bipartite graph is planar (K3,3 comes to mind).

## Are all 4-colorable graphs planar?

The Four Color Theorem states that every planar graph is properly 4-colorable. Moreover, it is well known that there are planar graphs that are non-4 -list colorable.

## Is there a nonplanar graph which admits a 4 coloring?

Every planar graph admits a 4-coloring, so any graph with chromatic number strictly grater than 4 cannot be planar. (f) False. Consider the bipartite graph K3,4. Its chromatic number is 2 but it is non planar.

## Which of the following graphs is not planar?

Example: The graphs shown in fig are non planar graphs. These graphs cannot be drawn in a plane so that no edges cross hence they are non-planar graphs.

## Who discovered the four color theorem?

In 1879 Alfred Kempe (1849-1922), using techniques similar to those described above, started from the ‘five neighbours property’ and developed a procedure known as the method of ‘Kempe Chains’ to find a proof of the Four Colour Theorem. He published this proof in the American Journal of Mathematics.

## Is the graph 4-colorable Why or why not?

Hence we have a contradiction, so we can conclude that the original hypothesis was false, i.e., there does not exist a graph that is not 4-colorable. The unavoidable set found by Appel and Haken consisted of nearly 1500 subgraphs, and many of these required considerable analysis to prove that they were “reducible”.

## How many colors should I color planar graph?

four colorsIn graph-theoretic terminology, the four-color theorem states that the vertices of every planar graph can be colored with at most four colors so that no two adjacent vertices receive the same color, or for short: Every planar graph is four-colorable.

## What is the three color problem?

This issue is a part of graph theory. It is well known that, given any separation of a plane into contiguous regions, producing a figure called a map, no more than four colors are required to color the regions of the map so that no two adjacent regions have the same color.