<< Chapter < Page Chapter >> Page >

Proposition 2:

| G | δ ( G ) Δ ( G ) .

Proof: We start by looking at the vertex with the smallest degree, v s . Since for any vertex v , N ( v ) N ( v s ) we can say that every vertex is connected to either v s or a vertex in N ( v s ) . There are δ ( G ) such vertices, having a maximum degree of Δ ( G ) , implying that there are at most δ G Δ ( G ) vertices in the graph.

Proposition 3 (the lonely neighbor property):

For each edge ( u , v ) there exists a vertex w such that exactly one of ( w , v ) or ( w , u ) is in E ( G ) . Assuming ( w , v ) is in E ( G ) then for each vertex y exactly one of ( y , w ) or ( y , u ) is in E ( G ) .

Proof: Let an edge ( u , v ) be given. Because our graph is minimal, there exists a vertex w such that N ( a ) N ( w ) = b for some labels a , b { u , v } . Without loss of generality assign a to u and b to v . Now suppose for the sake of contradiction that ( w , u ) is in E ( G ) . Then { u , v , w } induces a K 3 and so there exists x V ( G ) { u , v , w } such that { u , v , w , x } induces a K 4 , but then x N ( u ) N ( w ) = v a contradiction. Now let a vertex y V ( G ) { u , v , w } be given. Suppose both ( y , w ) and ( y , u ) are in E ( G ) then y N ( u ) N ( w ) = v which is again a contradiction.

Proposition 4:

For any edge ( u , v ) G , at least one of u , v has degree of at least 4.

Proof: Suppose that neither of u nor v have degree of at least 4. It follows from Proposition 1 that d e g ( u ) = d e g ( v ) = 3 . u and v must both be contained in a K 4 subgraph. By the lonely neighbor property, there must exist a vertex w such that either ( u , w ) G or ( v , w ) G . This is a contradiction, as desired.

Proposition 5:

For any induced K 4 subgraph, at most one vertex has degree 3.

Proof: This follows directly from Proposition 4.

Proposition 5:

If G ( V , E ) is a graph in S then there are atleast | E | 6 choices of 4-tuples which induce a K 4 .

Proof: Each edge is in a K 4 and so it must make up at least 1 6 of a K 4 .

Proposition 6:

For any v V ( G ) , v is contained in at least deg( v ) 3 K 4 subgraphs.

Proof: Since any K 4 subgraph that contains v must contain three other vertices, and v must be adjacent to all of these vertices, there must be deg( v ) 3 induced K 4 subgraphs. Since this implies that there may be some uncounted incident edges to v , and that all edges are contained in a K 4 subgraph, it follows that v is contained in at least deg( v ) 3 K 4 subgraphs.

Proposition 7:

In any induced K 4 subgraph, at least one vertex must have a minimum degree of 5.

Proof: Let { v 1 , v 2 , v 3 , v 4 } G induce a K 4 subgraph. Suppose for the sake of contradiction that d e g ( v i ) 4 , for i { 1 , 2 , 3 , 4 } . K 4 is not a minimal 3-cover, so without loss of generality, let v 1 have degree 4. Since all edges are contained in a K 4 subgraph, it follows that two more vertices in our original K 4 subgraph ( { v 2 , v 3 } ) must be part of another K 4 subgraph, along with v 1 , and a fifth vertex, called v 5 . v 4 cannot have degree of 4, since this would imply that at least one of { v 1 , v 2 , v 3 } would have degree more than 5, so it must have degree 3. However, the graph induced by { v 1 , v 2 , v 3 , v 4 , v 5 } is not a minimal 3-cover, so at least one incident edge must be added to v 5 . Call the corresponding adjacent vertex v 6 . Since G is a 3-cover, there must be a vertex that is adjacent to both v 3 and v 6 , which implies that we must add an incident edge to at least one of the vertices in { v 1 , v 2 , v 3 , v 4 } , which leads to a contradiction, as desired.


Future work on this topic could either find a counterexample to the conjecture, or show that there is no counterexample by using bounds to arrive at a contradiction.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, The art of the pfug. OpenStax CNX. Jun 05, 2013 Download for free at http://cnx.org/content/col10523/1.34
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'The art of the pfug' conversation and receive update notifications?