<bibliography>
 <citation type="article" key="Aaro2010">
  <author>Scott <surname>Aaronson</surname></author>
  <author>Alex <surname>Arkhipov</surname></author>
  <year>2013</year>
  <title>The Computational Complexity of Linear Optics</title>
  <journal>Theory of Computing</journal>
  <volume>9</volume>
  <number>4</number>
  <pages>143&#8211;252</pages>
  <doi>10.4086/toc.2013.v009a004</doi>
 </citation>
 <citation type="article" key="Ahar2004">
  <author>Dorit <surname>Aharonov</surname></author>
  <author>Wim <surname>van Dam</surname></author>
  <author>Julia <surname>Kempe</surname></author>
  <author>Zeph <surname>Landau</surname></author>
  <author>Seth <surname>Lloyd</surname></author>
  <author>Oded <surname>Regev</surname></author>
  <year>2007</year>
  <title>Adiabatic Quantum Computation is Equivalent to Standard Quantum Computation</title>
  <journal>SIAM Journal on Computing</journal>
  <volume>37</volume>
  <pages>166&#8211;194</pages>
  <doi>10.1137/S0097539705447323</doi>
 </citation>
 <citation type="article" key="Benn1997">
  <author>C. <surname>Bennett</surname></author>
  <author>E. <surname>Bernstein</surname></author>
  <author>G. <surname>Brassard</surname></author>
  <author>U. <surname>Vazirani</surname></author>
  <year>1997</year>
  <title>Strengths and Weaknesses of Quantum Computing</title>
  <journal>SIAM Journal on Computing</journal>
  <volume>26</volume>
  <number>5</number>
  <pages>1510&#8211;1523</pages>
  <doi>10.1137/S0097539796300933</doi>
 </citation>
 <citation type="article" key="Blum2002">
  <author>Robin <surname>Blume-Kohout</surname></author>
  <author>Carlton M. <surname>Caves</surname></author>
  <author>Ivan H. <surname>Deutsch</surname></author>
  <year>2002</year>
  <title>Climbing Mount Scalable: Physical Resource Requirements for a Scalable Quantum Computer</title>
  <journal>Found. Phys.</journal>
  <volume>32</volume>
  <number>11</number>
  <pages>1641&#8211;1670</pages>
  <doi>10.1023/A:1021471621587</doi>
 </citation>
 <citation type="article" key="Boug2016">
  <author>Hamza <surname>Bougroura</surname></author>
  <author>Habib <surname>Aissaoui</surname></author>
  <author>Nicholas <surname>Chancellor</surname></author>
  <author>Viv <surname>Kendon</surname></author>
  <year>2016</year>
  <title>Quantum-walk transport properties on graphene structures</title>
  <journal>Phys. Rev. A</journal>
  <volume>94</volume>
  <pages>062331</pages>
  <doi>10.1103/PhysRevA.94.062331</doi>
 </citation>
 <citation type="article" key="Broo2010">
  <author>M. A. <surname>Broome</surname></author>
  <author>A. <surname>Fedrizzi</surname></author>
  <author>B. P. <surname>Lanyon</surname></author>
  <author>I. <surname>Kassal</surname></author>
  <author>A. <surname>Aspuru-Guzik</surname></author>
  <author>A. G. <surname>White</surname></author>
  <year>2010</year>
  <title>Discrete single-photon quantum walks with tunable decoherence</title>
  <journal>Phys. Rev. Lett.</journal>
  <volume>104</volume>
  <pages>153602</pages>
  <doi>10.1103/PhysRevLett.104.153602</doi>
 </citation>
 <citation type="article" key="Brow2010">
  <author>K. L. <surname>Brown</surname></author>
  <author>W. J. <surname>Munro</surname></author>
  <author>V. M. <surname>Kendon</surname></author>
  <year>2010</year>
  <title>Using Quantum Computers for Quantum Simulation</title>
  <journal>Entropy</journal>
  <volume>12</volume>
  <number>11</number>
  <pages>2268&#8211;2307</pages>
  <doi>10.3390/e12112268</doi>
 </citation>
 <citation type="article" key="Call2019">
  <author>A <surname>Callison</surname></author>
  <author>N <surname>Chancellor</surname></author>
  <author>F <surname>Mintert</surname></author>
  <author>V <surname>Kendon</surname></author>
  <year>2019</year>
  <title>Finding spin glass ground states using quantum walks</title>
  <journal>New J. Phys.</journal>
  <volume>21</volume>
  <pages>123022</pages>
  <doi>10.1088/1367-2630/ab5ca2</doi>
 </citation>
 <citation type="misc" key="Chan2017">
  <author>N. <surname>Chancellor</surname></author>
  <year>2017</year>
  <title>Modernizing Quantum Annealing II: Genetic algorithms with the Inference Primitive Formalism</title>
  <url>https://arxiv.org/abs/1609.05875</url>
  <note>ArXiv:1609.05875</note>
 </citation>
 <citation type="article" key="Chan2016">
  <author>N. <surname>Chancellor</surname></author>
  <year>2017</year>
  <title>Modernizing Quantum Annealing using Local Searches</title>
  <journal>New J. Phys.</journal>
  <volume>19</volume>
  <number>2</number>
  <pages>023024</pages>
  <doi>10.1088/1367-2630/aa59c4</doi>
 </citation>
 <citation type="article" key="Chil2009">
  <author>Andrew M. <surname>Childs</surname></author>
  <year>2009</year>
  <title>Universal computation by quantum walk</title>
  <journal>Phys. Rev. Lett.</journal>
  <volume>102</volume>
  <pages>180501</pages>
  <doi>10.1103/PhysRevLett.102.180501</doi>
 </citation>
 <citation type="inproceedings" key="Chil2002">
  <author>Andrew M. <surname>Childs</surname></author>
  <author>Richard <surname>Cleve</surname></author>
  <author>Enrico <surname>Deotto</surname></author>
  <author>Edward <surname>Farhi</surname></author>
  <author>Sam <surname>Gutmann</surname></author>
  <author>Daniel A. <surname>Spielman</surname></author>
  <year>2003</year>
  <title>Exponential algorithmic speedup by a quantum walk</title>
  <booktitle>Proc. 35th Annual ACM Symposium on Theory of Computing (STOC 2003)</booktitle>
  <publisher>Assoc. for Comp. Machinery, New York</publisher>
  <pages>59&#8211;68</pages>
  <doi>10.1145/780542.780552</doi>
 </citation>
 <citation type="article" key="Chil2001">
  <author>Andrew M. <surname>Childs</surname></author>
  <author>Edward <surname>Farhi</surname></author>
  <author>John <surname>Preskill</surname></author>
  <year>2001</year>
  <title>Robustness of adiabatic quantum computation</title>
  <journal>Physical Review A</journal>
  <volume>65</volume>
  <number>1</number>
  <pages>012322</pages>
  <doi>10.1103/PhysRevA.65.012322</doi>
 </citation>
 <citation type="article" key="Chil2004">
  <author>Andrew M. <surname>Childs</surname></author>
  <author>Jeffrey <surname>Goldstone</surname></author>
  <year>2004</year>
  <title>Spatial search by quantum walk</title>
  <journal>Physical Review A</journal>
  <volume>70</volume>
  <number>2</number>
  <pages>022314</pages>
  <doi>10.1103/PhysRevA.70.022314</doi>
 </citation>
 <citation type="article" key="Chil2013">
  <author>Andrew M. <surname>Childs</surname></author>
  <author>David <surname>Gosset</surname></author>
  <author>Zak <surname>Webb</surname></author>
  <year>2013</year>
  <title>Universal computation by multi-particle quantum walk</title>
  <journal>Science</journal>
  <volume>339</volume>
  <pages>791&#8211;794</pages>
  <doi>10.1126/science.1229957</doi>
 </citation>
 <citation type="misc" key="Choi2010">
  <author>Vicky <surname>Choi</surname></author>
  <year>2010</year>
  <title>Adiabatic quantum algorithms for the NP-complete Maximum-Weight Independent set, Exact Cover and 3SAT problems</title>
  <url>https://arxiv.org/abs/1004.2226</url>
  <note>ArXiv:1004.2226</note>
 </citation>
 <citation type="article" key="Dodd2019">
  <author>A. Ben <surname>Dodds</surname></author>
  <author>Viv <surname>Kendon</surname></author>
  <author>Charles S. <surname>Adams</surname></author>
  <author>Nicholas <surname>Chancellor</surname></author>
  <year>2019</year>
  <title>Practical designs for permutation-symmetric problem Hamiltonians on hypercubes</title>
  <journal>Phys. Rev. A</journal>
  <volume>100</volume>
  <pages>032320</pages>
  <doi>10.1103/PhysRevA.100.032320</doi>
 </citation>
 <citation type="article" key="Eker1998">
  <author>A <surname>Ekert</surname></author>
  <author>J <surname>Jozsa</surname></author>
  <year>1998</year>
  <title>Quantum algorithms: entanglement–enhanced information processing</title>
  <journal>Phil. Trans. Royal Soc. A</journal>
  <volume>356</volume>
  <pages>1769&#8211;82</pages>
  <doi>10.1098/rsta.1998.0248</doi>
 </citation>
 <citation type="misc" key="Farh2000">
  <author>E. <surname>Farhi</surname></author>
  <author>J. <surname>Goldstone</surname></author>
  <author>S. <surname>Gutmann</surname></author>
  <author>M. <surname>Sipser</surname></author>
  <year>2000</year>
  <title>Quantum Computation by Adiabatic Evolution</title>
  <url>http://arxiv.org/quant-ph/abs/0001106</url>
  <note>ArXiv:quant-ph/0001106</note>
 </citation>
 <citation type="article" key="Farh1998">
  <author>E <surname>Farhi</surname></author>
  <author>S <surname>Gutmann</surname></author>
  <year>1998</year>
  <title>Quantum computation and decison trees</title>
  <journal>Phys. Rev. A</journal>
  <volume>58</volume>
  <pages>915&#8211;928</pages>
  <doi>10.1103/PhysRevA.58.915</doi>
 </citation>
 <citation type="article" key="Fini1994">
  <author>A. B. <surname>Finilla</surname></author>
  <author>M. A. <surname>Gomez</surname></author>
  <author>C. <surname>Sebenik</surname></author>
  <author>J. D. <surname>Doll</surname></author>
  <year>1994</year>
  <title>Quantum annealing: A new method for minimizing multidimensional functions</title>
  <journal>Chem. Phys. Lett.</journal>
  <volume>219</volume>
  <pages>343</pages>
  <doi>10.1016/0009-2614(94)00117-0</doi>
 </citation>
 <citation type="misc" key="Hard2001">
  <author>Lucien <surname>Hardy</surname></author>
  <year>2001</year>
  <title>Quantum theory from five reasonable axioms</title>
  <url>http://arxiv.org/quant-ph/abs/0101012</url>
  <note>ArXiv:quant-ph/0101012</note>
 </citation>
 <citation type="article" key="Hart1984">
  <author>A. <surname>Hartwig</surname></author>
  <author>F. <surname>Daske</surname></author>
  <author>S. <surname>Kobe</surname></author>
  <year>1984</year>
  <title>A recursive branch-and-bound algorithm for the exact ground state of Ising spin-glass models</title>
  <journal>Computer Physics Communications</journal>
  <volume>32</volume>
  <number>2</number>
  <pages>133 &#8211; 138</pages>
  <doi>10.1016/0010-4655(84)90066-3</doi>
 </citation>
 <citation type="article" key="Hors2014">
  <author>C. <surname>Horsman</surname></author>
  <author>S. <surname>Stepney</surname></author>
  <author>R. C. <surname>Wagner</surname></author>
  <author>V. <surname>Kendon</surname></author>
  <year>2014</year>
  <title>When does a Physical System Compute?</title>
  <journal>Proc. Roy. Soc. A</journal>
  <volume>470</volume>
  <number>2169</number>
  <pages>20140182</pages>
  <doi>10.1098/rspa.2014.0182</doi>
 </citation>
 <citation type="inproceedings" key="Hors2017">
  <author>D <surname>Horsman</surname></author>
  <author>V <surname>Kendon</surname></author>
  <author>S <surname>Stepney</surname></author>
  <author>P <surname>Young</surname></author>
  <year>2017</year>
  <title>Abstraction and representation in living organisms: when does a biological system compute?</title>
  <editor>Giovagnoli R <surname>Dodig-Crnkovic G</surname></editor>
  <booktitle>Representation and Reality in Humans, Other Living Organisms and Intelligent Machines</booktitle>
  <series>Studies in Applied Philosophy, Epistemology and Rational Ethics</series>
  <volume>28</volume>
  <publisher>Springer</publisher>
  <pages>91&#8211;116</pages>
  <doi>10.1007/978-3-319-43784-2_6</doi>
 </citation>
 <citation type="article" key="Hugh1997">
  <author>Richard I. G. <surname>Hughes</surname></author>
  <year>1997</year>
  <title>Models and representation</title>
  <journal>Philosophy of science</journal>
  <volume>64</volume>
  <pages>S325&#8211;S336</pages>
  <doi>10.1086/392611</doi>
 </citation>
 <citation type="article" key="Kado1998">
  <author>T. <surname>Kadowaki</surname></author>
  <author>H. <surname>Nishimori</surname></author>
  <year>1998</year>
  <title>Quantum annealing in the transverse Ising model</title>
  <journal>Phys. Rev. E</journal>
  <volume>58</volume>
  <pages>5355</pages>
  <doi>10.1103/PhysRevE.58.5355</doi>
 </citation>
 <citation type="article" key="Kars2009">
  <author>Michal <surname>Karski</surname></author>
  <author>Leonid <surname>Forster</surname></author>
  <author>Jai-Min <surname>Choi</surname></author>
  <author>Andreas <surname>Steffen</surname></author>
  <author>Wolfgang <surname>Alt</surname></author>
  <author>Dieter <surname>Meschede</surname></author>
  <author>Artur <surname>Widera</surname></author>
  <year>2009</year>
  <title>Quantum Walk in Position Space with Single Optically Trapped Atoms</title>
  <journal>Science</journal>
  <volume>325</volume>
  <number>5937</number>
  <pages>174&#8211;177</pages>
  <doi>10.1126/science.1174436</doi>
 </citation>
 <citation type="inproceedings" key="Kemp2004">
  <author><surname>Kempe</surname></author>
  <author><surname>Kitaev</surname></author>
  <author><surname>Regev</surname></author>
  <year>2004</year>
  <title>The Complexity of the Local Hamiltonian Problem</title>
  <editor>K. <surname>Lodaya</surname></editor>
  <editor>M. <surname>Mahajan</surname></editor>
  <booktitle>Proc. 24th FSTTCS</booktitle>
  <series>LNCS</series>
  <volume>3328</volume>
  <publisher>Springer</publisher>
  <pages>372&#8211;383</pages>
  <doi>10.1007/978-3-540-30538-5_31</doi>
 </citation>
 <citation type="inproceedings" key="Kend2011">
  <author>V. <surname>Kendon</surname></author>
  <author>A. <surname>Sebald</surname></author>
  <author>S. <surname>Stepney</surname></author>
  <author>M. <surname>Bechmann</surname></author>
  <author>P. <surname>Hines</surname></author>
  <author>R. C. <surname>Wagner</surname></author>
  <year>2011</year>
  <title>Heterotic computing</title>
  <editor>C.S. <surname>Calude</surname></editor>
  <editor>J. <surname>Kari</surname></editor>
  <editor>I. <surname>Petre</surname></editor>
  <editor>G. <surname>Rozenberg</surname></editor>
  <booktitle>Unconventional Computation, LNCS</booktitle>
  <volume>6714</volume>
  <publisher>Springer</publisher>
  <address>Berlin, Heidelberg</address>
  <pages>113&#8211;124</pages>
  <doi>10.1007/978-3-642-21341-0_16</doi>
 </citation>
 <citation type="proceedings" key="Kend2013">
  <editor>V <surname>Kendon</surname></editor>
  <editor>A <surname>Siebald</surname></editor>
  <editor>S <surname>Stepney</surname></editor>
  <year>2015</year>
  <title>Heterotic computing: exploiting hybrid computational devices</title>
  <series>Phil. Trans. Royal Soc. A</series>
  <volume>373</volume>
  <publisher>Royal Society</publisher>
  <address>London, UK</address>
  <doi>10.1098/rsta.2015.0091</doi>
 </citation>
 <citation type="misc" key="Kend2020">
  <author>Viv <surname>Kendon</surname></author>
  <year>2020</year>
  <title>How to compute using quantum walks</title>
  <doi>10.24350/CIRM.V.19600203</doi>
  <note>CIRM. Audiovisual resource.</note>
 </citation>
 <citation type="misc" key="Lida2019">
  <author>Daniel <surname>Lidar</surname></author>
  <year>2019</year>
  <title>Arbitrary-time error suppression for Markovian adiabatic quantum computing using stabilizer subspace codes</title>
  <url>http://arxiv.org/abs/1904.12028</url>
 </citation>
 <citation type="misc" key="Lode2019">
  <author>Bas <surname>Lodewijks</surname></author>
  <year>2019</year>
  <title>Mapping NP-hard and NP-complete optimisation problems to Quadratic Unconstrained Binary Optimisation problems</title>
  <url>http://arxiv.org/abs/1911.08043</url>
 </citation>
 <citation type="article" key="Love2010">
  <author>N. B. <surname>Lovett</surname></author>
  <author>S. <surname>Cooper</surname></author>
  <author>M. S. <surname>Everitt</surname></author>
  <author>M. <surname>Trevers</surname></author>
  <author>V. <surname>Kendon</surname></author>
  <year>2010</year>
  <title>Universal quantum computation using the discrete time quantum walk</title>
  <journal>Phys. Rev. A</journal>
  <volume>81</volume>
  <pages>042330</pages>
  <doi>10.1103/PhysRevA.81.042330</doi>
 </citation>
 <citation type="article" key="Mohs2008">
  <author>M. <surname>Mohseni</surname></author>
  <author>P. <surname>Rebentrost</surname></author>
  <author>S. <surname>Lloyd</surname></author>
  <author>A. <surname>Aspuru-Guzik</surname></author>
  <year>2008</year>
  <title>Environment-assisted quantum walks in photosynthetic energy transfer</title>
  <journal>J. Chem. Phys.</journal>
  <volume>129</volume>
  <pages>174106</pages>
  <doi>10.1063/1.3002335</doi>
 </citation>
 <citation type="article" key="Mont2015">
  <author>Ashley <surname>Montanaro</surname></author>
  <year>2018</year>
  <title>Quantum-Walk Speedup of Backtracking Algorithms</title>
  <journal>Theory of Computing</journal>
  <volume>14</volume>
  <number>15</number>
  <pages>1&#8211;24</pages>
  <doi>10.4086/toc.2018.v014a015</doi>
 </citation>
 <citation type="misc" key="Mont2019">
  <author>Ashley <surname>Montanaro</surname></author>
  <year>2019</year>
  <title>Quantum speedup of branch-and-bound algorithms</title>
  <url>http://arxiv.org/abs/1906.10375</url>
  <note>ArXiv:1906.10375</note>
 </citation>
 <citation type="article" key="Morl2019">
  <author>JG <surname>Morley</surname></author>
  <author>N <surname>Chancellor</surname></author>
  <author>S <surname>Bose</surname></author>
  <author>V <surname>Kendon</surname></author>
  <year>2019</year>
  <title>Quantum search with hybrid adiabatic-quantum walk algorithms and realistic noise</title>
  <journal>Phys. Rev. A</journal>
  <volume>99</volume>
  <pages>022339</pages>
  <doi>10.1103/PhysRevA.99.022339</doi>
 </citation>
 <citation type="article" key="Pere2008">
  <author>Hagai B. <surname>Perets</surname></author>
  <author>Yoav <surname>Lahini</surname></author>
  <author>Francesca <surname>Pozzi</surname></author>
  <author>Marc <surname>Sorel</surname></author>
  <author>Roberto <surname>Morandotti</surname></author>
  <author>Yaron <surname>Silberberg</surname></author>
  <year>2008</year>
  <title>Realization of quantum walks with negligible decoherence in waveguide lattices</title>
  <journal>Phys. Rev. Lett.</journal>
  <volume>100</volume>
  <pages>170506</pages>
  <doi>10.1103/PhysRevLett.100.170506</doi>
 </citation>
 <citation type="incollection" key="Picc2017">
  <author>Gualtiero <surname>Piccinini</surname></author>
  <year>2017</year>
  <title>Computation in Physical Systems</title>
  <editor>Edward N. <surname>Zalta</surname></editor>
  <booktitle>The Stanford Encyclopedia of Philosophy</booktitle>
  <edition>Summer 2017</edition>
  <publisher>Stanford University Press</publisher>
  <url>http://plato.stanford.edu/archives/sum2017/entries/computation-physicalsystems/</url>
 </citation>
 <citation type="book" key="Putn1988">
  <author>Hilary <surname>Putnam</surname></author>
  <year>1988</year>
  <title>Representation and Reality</title>
  <publisher>MIT Press</publisher>
  <address>Cambridge, MA</address>
  <url>https://mitpress.mit.edu/books/representation-and-reality</url>
  <note>ISBN: 9780262161084</note>
 </citation>
 <citation type="article" key="Rola2002">
  <author>J&#233;r&#233;mie <surname>Roland</surname></author>
  <author>Nicolas J. <surname>Cerf</surname></author>
  <year>2002</year>
  <title>Quantum search by local adiabatic evolution</title>
  <journal>Phys. Rev. A</journal>
  <volume>65</volume>
  <pages>042308</pages>
  <doi>10.1103/PhysRevA.65.042308</doi>
 </citation>
 <citation type="article" key="Ryan2005">
  <author>C. A. <surname>Ryan</surname></author>
  <author>M. <surname>Laforest</surname></author>
  <author>J. C. <surname>Boileau</surname></author>
  <author>R. <surname>Laflamme</surname></author>
  <year>2005</year>
  <title>Experimental implementation of discrete time quantum random walk on an NMR quantum information processor</title>
  <journal>Phys. Rev. A</journal>
  <volume>72</volume>
  <pages>062317</pages>
  <doi>10.1103/PhysRevA.72.062317</doi>
 </citation>
 <citation type="article" key="Schr2011">
  <author>A. <surname>Schreiber</surname></author>
  <author>K. N. <surname>Cassemiro</surname></author>
  <author>V. <surname>Poto&#x010d;ek</surname></author>
  <author>A. <surname>G&#225;bris</surname></author>
  <author>I. <surname>Jex</surname></author>
  <author>Ch. <surname>Silberhorn</surname></author>
  <year>2011</year>
  <title>Decoherence and disorder in quantum walks: From ballistic spread to localization</title>
  <journal>Phys. Rev. Lett.</journal>
  <volume>106</volume>
  <pages>180403</pages>
  <doi>10.1103/PhysRevLett.106.180403</doi>
 </citation>
 <citation type="article" key="Shen2002">
  <author>Neil <surname>Shenvi</surname></author>
  <author>Julia <surname>Kempe</surname></author>
  <author>K <surname>Birgitta Whaley</surname></author>
  <year>2003</year>
  <title>A quantum random walk search algorithm</title>
  <journal>Phys. Rev. A</journal>
  <volume>67</volume>
  <pages>052307</pages>
  <doi>10.1103/PhysRevA.67.052307</doi>
 </citation>
 <citation type="article" key="Steff2003">
  <author><surname>Steffen</surname></author>
  <author><surname>vanDam</surname></author>
  <author><surname>Hogg</surname></author>
  <author><surname>Breyta</surname></author>
  <author><surname>Chuang</surname></author>
  <year>2003</year>
  <title>Experimental implementation of an adiabatic quantum optimization algorithm</title>
  <journal>Phys. Rev. Lett.</journal>
  <volume>90</volume>
  <number>6</number>
  <pages>067903</pages>
  <doi>10.1103/PhysRevLett.90.067903</doi>
 </citation>
 <citation type="inproceedings" key="Step2019">
  <author>S. <surname>Stepney</surname></author>
  <author>V. <surname>Kendon</surname></author>
  <year>2019</year>
  <title>The role of the representational entity in physical computing</title>
  <booktitle>UCNC 2019, Tokyo, Japan, June 2019</booktitle>
  <series>LNCS</series>
  <volume>11493</volume>
  <publisher>Springer</publisher>
  <pages>219&#8211;231</pages>
  <doi>10.1007/978-3-030-19311-9_18</doi>
 </citation>
 <citation type="incollection" key="Wies2008">
  <author>K. <surname>Wiesner</surname></author>
  <year>2009</year>
  <title>Quantum Cellular Automata</title>
  <editor>Robert A. <surname>Meyers</surname></editor>
  <booktitle>Springer Encyclopedia of Complexity and System Science</booktitle>
  <chapter>Cellular Automata, Mathematical Basis of, Ed. Andy Adamatzky</chapter>
  <publisher>Springer</publisher>
  <pages>00105</pages>
  <doi>10.1007/978-0-387-30440-3_426</doi>
  <note>or http://arxiv.org/abs/0808.0679</note>
 </citation>
</bibliography>
