交叉數:修订间差异
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{{Translating|[[:en:Crossing number (graph theory)]]||tpercent=41.3|time=2021-06-24T20:16:25+00:00}} |
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在[[圖論]],'''交叉數'''是指一個[[圖]]在[[平面 (数学)|平面]]上,邊的交叉點的最小數目。 |
在[[圖論]],'''交叉數'''是指一個[[圖]]在[[平面 (数学)|平面]]上,邊的交叉點的最小數目。 |
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給定一個圖,計算其交叉數是一個[[NP-hard]]的問題(1983年)。 |
給定一個圖,計算其交叉數是一個[[NP-hard]]的問題(1983年)。 |
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如女口Without further qualification, the crossing number allows drawings in which the edges may be represented by arbitrary curves. A variation of this concept, the '''rectilinear crossing number''', requires all edges to be straight line segments, and may differ from the crossing number. In particular, the rectilinear crossing number of a [[complete graph]] is essentially the same as the minimum number of [[convex polygon|convex]] [[quadrilaterals]] determined by a set of {{mvar|n}} points in general position. The problem of determining this number is closely related to the [[happy ending problem]].{{r|sw}} |
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==特殊情況== |
==特殊情況== |
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截止2015年4月,僅得很少幾類圖的交叉數為人所知。即使是[[完全圖]]、[[完全二部圖]]、兩個[[環 (圖論)|環]]的積等結構較簡單的圖,也僅得初始幾個的交叉數是已知的,但交叉數的下界方面,已有一定進展。{{r|kmprs}} |
截止2015年4月,僅得很少幾類圖的交叉數為人所知。即使是[[完全圖]]、[[完全二部圖]]、兩個[[環 (圖論)|環]]的積等結構較簡單的圖,也僅得初始幾個的交叉數是已知的,但交叉數的下界方面,已有一定進展。{{r|kmprs}} |
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2009年,{{link-en|愛德華·柏奇|Ed Pegg}}<!--遵循[[西蒙·柏奇]]的先例-->和Geoffrey Exoo<!--未能查證讀音-->猜想交叉數為13的最小立方圖為{{link-en|塔特-考克斯特圖|Tutte–Coxeter graph}}<!--按英文維基百科[[W. T. Tutte]]標注的讀音依[[WP: 外語譯音表/英語]]暫譯-->,以及交叉數為170的最小立方圖為{{link-en|塔特12-籠|Tutte 12-cage}}。{{r|pe|exoo}} |
2009年,{{link-en|愛德華·柏奇|Ed Pegg}}<!--遵循[[西蒙·柏奇]]的先例-->和Geoffrey Exoo<!--未能查證讀音-->猜想交叉數為13的最小立方圖為{{link-en|塔特-考克斯特圖|Tutte–Coxeter graph}}<!--按英文維基百科[[W. T. Tutte]]標注的讀音依[[WP: 外語譯音表/英語]]暫譯-->,以及交叉數為170的最小立方圖為{{link-en|塔特12-籠|Tutte 12-cage}}。{{r|pe|exoo}} |
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==複雜度與近似== |
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一般情況下,很難計算圖的交叉數。{{link-en|米高·加里|Michael Garey}}<!--參考地名[[加里 (加利福尼亞州)]]暫譯-->和{{link-en|大衛·詹森|David S. Johnson}}於1983年證明了計算交叉數是[[NP難]]問題。{{r|gj}}即使僅考慮[[立方圖]]{{r|hlineny}},或者僅考慮將近平面的特殊情況(即可藉刪走一條邊使之變成平面圖){{r|cm}},問題仍然NP難。另一個相關問題是計算僅能使用直線段畫圖時,交叉數目的最小值。該最小值稱為'''直線交叉數'''(rectilinear crossing number)。該問題對於{{link-en|實數的存在理論|existential theory of the reals}}是[[完備 (複雜度)|完全]]的。{{r|ER}} |
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另一方面,對於固定的常數{{mvar|k}},有高效算法判定交叉數是否小於{{mvar|k}}。換言之,交叉數問題是{{link-en|固定參數可馴順|fixed-parameter tractable}}<!--tractable的譯法參考张鸿林、葛显良《英汉数学词汇》-->的。{{r|grohe|kr}}但若{{mvar|k}}不是常數,而是與輸入大小有關的函數,例如{{math|1=''k'' = {{!}}''V''{{!}}/2}},則問題仍然很難。對於度數有界的圖{{math|''G''}},有高效的[[近似算法]]能夠近似計算交叉數{{math|cr(''G'')}}。{{r|egs}}實務上,常使用[[啟發法|啟發式]]算法,例如從空圖開始,逐條邊加入,使得每次產生的交叉數儘可能小。直線交叉數[[分布式计算]]計劃(Rectilinear Crossing Number project)使用了此類算法。{{r|rcnp}} |
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==交叉數不等式== |
==交叉數不等式== |
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{{Main |
{{Main |
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<ref name=bt>{{cite arXiv |first1=János |last1=Barát |first2=Géza |last2=Tóth |year=2009 |title=Towards the Albertson Conjecture |eprint=0909.0413 |class=math.CO}}</ref> |
<ref name=bt>{{cite arXiv |first1=János |last1=Barát |first2=Géza |last2=Tóth |year=2009 |title=Towards the Albertson Conjecture |eprint=0909.0413 |class=math.CO}}</ref> |
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<ref name=cm>{{cite journal |author=Cabello S. and [[Bojan Mohar|Mohar B.]] |title=Adding One Edge to Planar Graphs Makes Crossing Number and 1-Planarity Hard |year=2013 |journal=[[SIAM Journal on Computing]] |volume=42 |issue=5 |pages=1803–1829 |doi=10.1137/120872310 |arxiv=1203.5944 |s2cid=6535755 }}</ref> |
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<ref name=egs>{{Cite journal |first1=Guy |last1=Even |first2=Sudipto |last2=Guha |first3 = Baruch | last3 = Schieber | title=Improved Approximations of Crossings in Graph Drawings and VLSI Layout Areas |journal=[[SIAM Journal on Computing]] |volume=32 |year=2003 |pages=231–252 |doi=10.1137/S0097539700373520 |issue=1 }}</ref> |
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<ref name=ER>{{Cite conference| first=Marcus| last=Schaefer| title=Complexity of some geometric and topological problems|url=http://ovid.cs.depaul.edu/documents/convex.pdf|conference=[[International Symposium on Graph Drawing|Graph Drawing, 17th International Symposium, GS 2009, Chicago, IL, USA, September 2009, Revised Papers]]|series=Lecture Notes in Computer Science|publisher=Springer-Verlag| volume=5849| pages=334–344| doi=10.1007/978-3-642-11805-0_32 |year=2010|isbn=978-3-642-11804-3|doi-access=free}}.</ref> |
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<ref name=exoo>{{cite web |last=Exoo |first=G. |url=http://isu.indstate.edu/ge/COMBIN/RECTILINEAR/ |title=Rectilinear Drawings of Famous Graphs}}</ref> |
<ref name=exoo>{{cite web |last=Exoo |first=G. |url=http://isu.indstate.edu/ge/COMBIN/RECTILINEAR/ |title=Rectilinear Drawings of Famous Graphs}}</ref> |
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| title = Proof Techniques in Graph Theory (Proc. Second Ann Arbor Graph Theory Conf., Ann Arbor, Mich., 1968) |
| title = Proof Techniques in Graph Theory (Proc. Second Ann Arbor Graph Theory Conf., Ann Arbor, Mich., 1968) |
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| year = 1969}}.</ref> |
| year = 1969}}.</ref> |
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<ref name=gj>{{cite journal |author1=Garey, M. R. |author-link=Michael Garey |author2=Johnson, D. S. |author2-link=David S. Johnson |title=Crossing number is NP-complete |journal=SIAM Journal on Algebraic and Discrete Methods |volume=4 |pages=312–316 |year=1983 |mr=0711340 |doi=10.1137/0604033 |issue=3 }}</ref> |
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<ref name=grohe>{{Cite journal |last=Grohe |first=M.|author-link=Martin Grohe |title=Computing crossing numbers in quadratic time |journal=[[Journal of Computer and System Sciences]]|volume=68 |issue=2 |year=2005 |pages=285–302 |mr=2059096 |doi=10.1016/j.jcss.2003.07.008 |arxiv=cs/0009010 }}</ref> |
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<ref name=hlineny>{{cite journal |author=Hliněný, P. |title=Crossing number is hard for cubic graphs |year=2006 |journal=[[Journal of Combinatorial Theory]]|series=Series B |volume=96 |issue=4 |pages=455–471 |mr=2232384 | doi=10.1016/j.jctb.2005.09.009 }}</ref> |
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<ref name=hn>{{citation|first1=Michael|last1=Haythorpe|first2=Alex|last2=Newcombe|title=There are no Cubic Graphs on 26 Vertices with Crossing Number 11|year=2018|arxiv=1804.10336}}</ref> |
<ref name=hn>{{citation|first1=Michael|last1=Haythorpe|first2=Alex|last2=Newcombe|title=There are no Cubic Graphs on 26 Vertices with Crossing Number 11|year=2018|arxiv=1804.10336}}</ref> |
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<ref name=kmprs>{{Cite journal |last1=de Klerk |first1=E. |last2=Maharry |first2=J. |last3=Pasechnik |first3=D. V. |last4=Richter |first4=B. |last5=Salazar |first5=G. |year=2006 |url=https://research.tilburguniversity.edu/en/publications/improved-bounds-for-the-crossing-numbers-of-kmn-and-kn |title=Improved bounds for the crossing numbers of ''K<sub>m,n</sub>'' and ''K<sub>n</sub>'' |journal=[[SIAM Journal on Discrete Mathematics]] |volume=20 |issue=1 |pages=189–202 | doi=10.1137/S0895480104442741 |arxiv=math/0404142 |s2cid=1509054 }}</ref> |
<ref name=kmprs>{{Cite journal |last1=de Klerk |first1=E. |last2=Maharry |first2=J. |last3=Pasechnik |first3=D. V. |last4=Richter |first4=B. |last5=Salazar |first5=G. |year=2006 |url=https://research.tilburguniversity.edu/en/publications/improved-bounds-for-the-crossing-numbers-of-kmn-and-kn |title=Improved bounds for the crossing numbers of ''K<sub>m,n</sub>'' and ''K<sub>n</sub>'' |journal=[[SIAM Journal on Discrete Mathematics]] |volume=20 |issue=1 |pages=189–202 | doi=10.1137/S0895480104442741 |arxiv=math/0404142 |s2cid=1509054 }}</ref> |
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<ref name=nabla>{{Cite journal |title=A combinatorial problem |first1=R. K. |last1=Guy |author-link=Richard K. Guy |journal=Nabla (Bulletin of the Malayan Mathematical Society) |volume=7 |year=1960 |pages=68–72 }}</ref> |
<ref name=nabla>{{Cite journal |title=A combinatorial problem |first1=R. K. |last1=Guy |author-link=Richard K. Guy |journal=Nabla (Bulletin of the Malayan Mathematical Society) |volume=7 |year=1960 |pages=68–72 }}</ref> |
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<ref name=kr>{{Cite conference |first1= Ken-ichi |last1=Kawarabayashi | author1-link = Ken-ichi Kawarabayashi |first2=Bruce |last2=Reed | author2-link = Bruce Reed (mathematician) |title=Computing crossing number in linear time |conference=[[Symposium on Theory of Computing|Proceedings of the 29th Annual ACM Symposium on Theory of Computing]] |year=2007 |pages=382–390 |doi=10.1145/1250790.1250848 |isbn= 978-1-59593-631-8}}</ref> |
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<ref name=mathworld>{{MathWorld|urlname=GraphCrossingNumber|title=Graph Crossing Number}}</ref> |
<ref name=mathworld>{{MathWorld|urlname=GraphCrossingNumber|title=Graph Crossing Number}}</ref> |
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<ref name=ps>{{cite book | last1 = Pach | first1 = János | author1-link = János Pach | last2 = Sharir | first2 = Micha | author2-link = Micha Sharir | contribution = 5.1 Crossings—the Brick Factory Problem | pages = 126–127 | publisher = [[American Mathematical Society]] | series = Mathematical Surveys and Monographs | title = Combinatorial Geometry and Its Algorithmic Applications: The Alcalá Lectures | volume = 152| year = 2009}}</ref> |
<ref name=ps>{{cite book | last1 = Pach | first1 = János | author1-link = János Pach | last2 = Sharir | first2 = Micha | author2-link = Micha Sharir | contribution = 5.1 Crossings—the Brick Factory Problem | pages = 126–127 | publisher = [[American Mathematical Society]] | series = Mathematical Surveys and Monographs | title = Combinatorial Geometry and Its Algorithmic Applications: The Alcalá Lectures | volume = 152| year = 2009}}</ref> |
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<ref name=rcnp>{{cite web |url=http://www.ist.tugraz.at/staff/aichholzer/research/rp/triangulations/crossing/ |archive-url=https://archive.is/20121230191705/http://www.ist.tugraz.at/staff/aichholzer/research/rp/triangulations/crossing/ |url-status=dead |archive-date=2012-12-30 |title=Rectilinear Crossing Number project |author=Oswin Aichholzer }}, and |
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[http://dist.ist.tugraz.at/cape5/ Rectilinear Crossing Number] on the Institute for Software Technology at Graz, University of Technology (2009).</ref> |
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<ref name=z>{{cite journal |last=Zarankiewicz |first=K. |author-link=Kazimierz Zarankiewicz|title=On a Problem of P. Turán Concerning Graphs |journal=[[Fundamenta Mathematicae]] |volume=41 |pages=137–145 |year=1954 |doi=10.4064/fm-41-1-137-145 |doi-access=free }}</ref> |
<ref name=z>{{cite journal |last=Zarankiewicz |first=K. |author-link=Kazimierz Zarankiewicz|title=On a Problem of P. Turán Concerning Graphs |journal=[[Fundamenta Mathematicae]] |volume=41 |pages=137–145 |year=1954 |doi=10.4064/fm-41-1-137-145 |doi-access=free }}</ref> |
2021年6月25日 (五) 21:23的版本
此條目目前正依照en:Crossing number (graph theory)上的内容进行翻译。 (2021年6月24日) |
一個圖在平面上可以有多種畫法,若有多於兩條邊相交於同一點,每對相交邊計算一次。
以表示圖的交叉數。若,稱為平面圖。
給定一個圖,計算其交叉數是一個NP-hard的問題(1983年)。
如女口Without further qualification, the crossing number allows drawings in which the edges may be represented by arbitrary curves. A variation of this concept, the rectilinear crossing number, requires all edges to be straight line segments, and may differ from the crossing number. In particular, the rectilinear crossing number of a complete graph is essentially the same as the minimum number of convex quadrilaterals determined by a set of n points in general position. The problem of determining this number is closely related to the happy ending problem.[1]
特殊情況
截止2015年4月,僅得很少幾類圖的交叉數為人所知。即使是完全圖、完全二部圖、兩個環的積等結構較簡單的圖,也僅得初始幾個的交叉數是已知的,但交叉數的下界方面,已有一定進展。[2]
完全二部圖
在第二次世界大戰期間,匈牙利數學家圖蘭·帕爾被迫在磚廠工作,要將一車車的磚從窯爐推到貨倉。工廠的每個窯爐到每個貨倉之間各有一條路軌,而磚車在路軌交叉處特別難推。於是,圖蘭提出其磚廠問題:窯爐、貨倉和路軌應如何安排,才能使交叉的數目最少?數學上,窯爐和貨倉可視為完全二部圖的頂點,而路軌則是二部圖的邊。於是工廠的佈局就是該圖在平面上的一個畫法,換言之問題變成: 完全二部圖的畫法中,交叉的最少數目是多少?[3]
卡齊米日·扎蘭凱維奇嘗試解決圖蘭磚廠問題,[4]但其證明有錯。不過,他成功推導出完全二部圖交叉數的一個上界:
一個猜想是,上述上界確實是所有完全二部圖的交叉數。[5]
完全圖與圖染色
完全圖的交叉數問題最先由安東尼·希爾提出,並於1960年出版。[6]希爾及其合作者約翰·恩斯特皆為對數學甚感興趣的構成主義藝術家。兩位不僅提出了問題,還猜想了該交叉數的公式,公式由理查·蓋於1960年出版。[6]具體來說,已知總有一種畫法,其交叉的數目為
上式在時,取值分別為,見整數數列線上大全的A000241號數列。希爾等人猜想,不存在更好的畫法,即上式給出了完全圖的交叉數。湯瑪士·沙提於1964年獨立地作出了同一個猜想。[7]
對於,沙提驗證了上式確實給出交叉的最小可能數目。潘(Shengjun Pan)和布魯斯·里希特(Bruce Richter)驗證了的情況。[8]
2007年,米高·艾伯森(Michael O. Albertson)提出了艾伯森猜想,其斷言:在所有色數為的圖之中,完全圖的交叉數最小。換言之,若此猜想與上段的猜想均成立,則每個染色數為的圖,交叉數皆不小於上段的公式。現已證明,艾伯森猜想對於成立。[9]
立方圖
已知交叉數為至的最小的立方圖,其頂點數分別為(OEIS數列A110507),如下表所記:
交叉數 | 最小立方圖例子 | 頂點數 |
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1 | 完全二部圖 | 4 |
2 | 佩特森圖 | 10 |
3 | 希伍德圖 | 14 |
4 | 莫比烏斯-坎特圖 | 16 |
5 | 帕普斯圖 | 18 |
6 | 笛沙格圖 | 20 |
7 | 有4個不同構的例子,但並無熟知命名[10] | 22 |
8 | 瑙魯圖、麥基圖、(3,7)-籠圖[11] | 24 |
9 | 麥基圖加某一條邊[12] | 26 |
10 | 麥基圖加某兩條邊[12] | 28 |
11 | 考克斯特圖[13] | 28 |
2009年,愛德華·柏奇和Geoffrey Exoo猜想交叉數為13的最小立方圖為塔特-考克斯特圖,以及交叉數為170的最小立方圖為塔特12-籠。[11][14]
複雜度與近似
一般情況下,很難計算圖的交叉數。米高·加里和大衛·詹森於1983年證明了計算交叉數是NP難問題。[15]即使僅考慮立方圖[16],或者僅考慮將近平面的特殊情況(即可藉刪走一條邊使之變成平面圖)[17],問題仍然NP難。另一個相關問題是計算僅能使用直線段畫圖時,交叉數目的最小值。該最小值稱為直線交叉數(rectilinear crossing number)。該問題對於實數的存在理論是完全的。[18]
另一方面,對於固定的常數k,有高效算法判定交叉數是否小於k。換言之,交叉數問題是固定參數可馴順的。[19][20]但若k不是常數,而是與輸入大小有關的函數,例如k = |V|/2,則問題仍然很難。對於度數有界的圖G,有高效的近似算法能夠近似計算交叉數cr(G)。[21]實務上,常使用啟發式算法,例如從空圖開始,逐條邊加入,使得每次產生的交叉數儘可能小。直線交叉數分布式计算計劃(Rectilinear Crossing Number project)使用了此類算法。[22]
交叉數不等式
交叉數不等式說明了給定邊數目和頂點數目,的下界。
已知平面圖都符合(歐拉公式)。考慮邊面的對應數目,每條邊剛好屬於某兩個面,而每個面最小有三條邊,因此對於平面圖有。為了消去,代入,得。
再考慮一般圖,如何將它「變成」平面圖。如果我們在每個相交點,都去掉一條邊,則剩下的圖必是平面圖。這個新的平面圖的邊數目為,而頂點數目v不變。因此,對於所有的圖都有
接下來使用機率方法,從G中構作一個新的圖。考慮在G所有頂點中選取某些點作為新圖G'的頂點;若G中的某一條邊的兩個端點都在V(G')內,則E(G')亦有該條邊;因此,G中的一個交點仍然存在在G'中的條件,是該交點涉及的2條邊的4個不同端點都保留在G'中。現在隨機選取G中的pv個頂點(),則 ,代入上面的不等式:
求的下界,希望能使上面的不等式右方儘可能大。
當相當大時,考慮,可以取,整理後得:
參考
- ^ 引用错误:没有为名为
sw
的参考文献提供内容 - ^ de Klerk, E.; Maharry, J.; Pasechnik, D. V.; Richter, B.; Salazar, G. Improved bounds for the crossing numbers of Km,n and Kn. SIAM Journal on Discrete Mathematics. 2006, 20 (1): 189–202. S2CID 1509054. arXiv:math/0404142 . doi:10.1137/S0895480104442741.
- ^ Pach, János; Sharir, Micha. 5.1 Crossings—the Brick Factory Problem. Combinatorial Geometry and Its Algorithmic Applications: The Alcalá Lectures. Mathematical Surveys and Monographs 152. American Mathematical Society. 2009: 126–127.
- ^ Zarankiewicz, K. On a Problem of P. Turán Concerning Graphs. Fundamenta Mathematicae. 1954, 41: 137–145. doi:10.4064/fm-41-1-137-145 .
- ^ Guy, Richard K. The decline and fall of Zarankiewicz's theorem. Proof Techniques in Graph Theory (Proc. Second Ann Arbor Graph Theory Conf., Ann Arbor, Mich., 1968). Academic Press, New York. 1969: 63–69. MR 0253931..
- ^ 6.0 6.1 Guy, R. K. A combinatorial problem. Nabla (Bulletin of the Malayan Mathematical Society). 1960, 7: 68–72.
- ^ Saaty, T.L. The minimum number of intersections in complete graphs. Proceedings of the National Academy of Sciences of the United States of America. 1964, 52 (3): 688–690. Bibcode:1964PNAS...52..688S. PMC 300329 . PMID 16591215. doi:10.1073/pnas.52.3.688.
- ^ Pan, Shengjun; Richter, R. Bruce. The crossing number of K11 is 100. Journal of Graph Theory. 2007, 56 (2): 128–134. MR 2350621. doi:10.1002/jgt.20249..
- ^ Barát, János; Tóth, Géza. Towards the Albertson Conjecture. 2009. arXiv:0909.0413 [math.CO].
- ^ 埃里克·韦斯坦因. Graph Crossing Number. MathWorld.
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