|. Since, |. ?. , |. ?. , and |. , for any 1 ? i ? l ? 1, there is |Y ? S l | < |Y ? S i |, for any 1 ? i ? l ? 1. Now, by Equation 7.3, for any 1 ? i ? l ? 1

K. Aardal, C. Van-hoesel, A. Koster, C. Mannino, and A. Sassano, Models and solution techniques for the frequency assignement problem, pp.261-317, 2003.

I. Abraham, C. Gavoille, and D. Malkhi, Compact Routing for Graphs Excluding a Fixed Minor, Proceedings of DISC 2005, pp.442-456, 2005.
DOI : 10.1007/11561927_32

URL : https://hal.archives-ouvertes.fr/hal-00378466

S. Arnborg, D. G. Corneil, and A. Proskurowski, -Tree, SIAM Journal on Algebraic Discrete Methods, vol.8, issue.2
DOI : 10.1137/0608024

S. Arnborg and A. Proskurowski, Linear time algorithms for NP-hard problems restricted to partial k-trees, Discrete Applied Mathematics, vol.23, issue.1, pp.11-24, 1989.
DOI : 10.1016/0166-218X(89)90031-0

L. Barrire, P. Fraigniaud, N. Santoro, and D. M. Thilikos, Searching Is Not Jumping, Proceedings of WG 2003, pp.34-45, 2003.
DOI : 10.1007/978-3-540-39890-5_4

L. Barrire, P. Flocchini, P. Fraigniaud, and N. Santoro, Connected Treewidth and Connected Graph Searching, Proceedings of SPAA 2002, pp.200-209, 2002.

A. Berry and J. P. Bordat, Separability generalizes Dirac's theorem, Discrete Applied Mathematics, vol.84, issue.1-3, pp.43-53, 1998.
DOI : 10.1016/S0166-218X(98)00005-5

A. Berry and J. P. Bordat, Local LexBFS Properties in an Arbitrary Graph, Proceedings of Journes Informatiques Messines, 2000.

A. Berry, P. Heggernes, and Y. Villanger, A Vertex Incremental Approach for Dynamically Maintaining Chordal Graphs, Proceedings of ISAAC 2003, pp.47-57, 2003.
DOI : 10.1007/978-3-540-24587-2_7

A. Bieszczad, B. Pagurek, and T. White, Mobile agents for network management, IEEE Communications Surveys & Tutorials, vol.1, issue.1, 1998.
DOI : 10.1109/COMST.1998.5340400

J. R. Blair and B. Peyton, An introduction to chordal graphs and clique trees. Graph Theory and Sparse Matrix Computations, pp.1-29, 1993.

H. L. Bodlaender, A tourist guide through treewidth, Acta Cybernetica, vol.11, pp.1-23, 1993.

H. L. Bodlaender, A Linear-Time Algorithm for Finding Tree-Decompositions of Small Treewidth, SIAM Journal on Computing, vol.25, issue.6, pp.1305-1317, 1996.
DOI : 10.1137/S0097539793251219

H. Bodlaender, A partial k-arboretum of graphs with bounded treewidth, Theoretical Computer Science, vol.209, issue.1-2, pp.1-45, 1998.
DOI : 10.1016/S0304-3975(97)00228-4

H. Bodlaender and F. Fomin, Approximation of pathwidth of outerplanar graphs, Journal of Algorithms, vol.43, issue.2, pp.190-200, 2002.
DOI : 10.1016/S0196-6774(02)00001-9

H. Bodlaender and T. Kloks, Efficient and Constructive Algorithms for the Pathwidth and Treewidth of Graphs, Journal of Algorithms, vol.21, issue.2, pp.358-402, 1996.
DOI : 10.1006/jagm.1996.0049

H. L. Bodlaender, T. Kloks, and D. Kratsch, Treewidth and Pathwidth of Permutation Graphs, SIAM Journal on Discrete Mathematics, vol.8, issue.4, pp.606-616, 1995.
DOI : 10.1137/S089548019223992X

H. L. Bodlaender and A. Koster, Safe separators for treewidth, Discrete Mathematics, vol.306, issue.3, 2003.
DOI : 10.1016/j.disc.2005.12.017

H. L. Bodlaender and D. Thilikos, Treewidth for graphs with small chordality, Discrete Applied Mathematics, vol.79, issue.1-3, pp.45-61, 1997.
DOI : 10.1016/S0166-218X(97)00031-0

J. C. Boland and C. G. Lekkerkerker, Representation of a finite graph by a set of intervals on the real line, Fundamenta Mathematicae, vol.51, pp.45-64, 1962.

K. Booth and G. Leuker, Testing for the consecutive ones property, interval graphs, and graph planarity using PQ-tree algorithms, Journal of Computer and System Sciences, vol.13, issue.3, pp.335-379, 1976.
DOI : 10.1016/S0022-0000(76)80045-1

V. Bouchitt and I. Todinca, Approximating the treewidth of AT-free graphs, Discrete Applied Mathematics, vol.131, issue.1, pp.11-37, 2003.
DOI : 10.1016/S0166-218X(02)00414-6

V. Bouchitté and I. Todinca, Treewidth and Minimum Fill-in: Grouping the Minimal Separators, SIAM Journal on Computing, vol.31, issue.1, pp.212-232, 2001.
DOI : 10.1137/S0097539799359683

H. Broersma, E. Dahlhaus, and T. Kloks, Algorithms for treewidth and minimum fill-in of HHDfree graphs, Proceedings of WG 1997, pp.109-117, 1997.

H. Broersma, E. Dahlhaus, and T. Kloks, A linear time algorithm for minimum fill-in and treewidth for distance hereditary graphs, Discrete Applied Mathematics, vol.99, issue.1-3, pp.367-400, 2000.
DOI : 10.1016/S0166-218X(99)00146-8

L. Cai, Fixed-parameter tractability of graph modification problems for hereditary properties, Information Processing Letters, vol.58, issue.4, pp.171-176, 1996.
DOI : 10.1016/0020-0190(96)00050-6

P. Z. Chinn, J. Chvátalová, A. K. Dewdney, and N. E. Gibbs, The bandwidth problem for graphs and matrices???a survey, Journal of Graph Theory, vol.17, issue.3, pp.223-254, 1982.
DOI : 10.1002/jgt.3190060302

B. Courcelle, THe monadic second-order logic on graphs III: Treewidth, forbidden minors and complexity issues, Informatique Théorique, vol.26, pp.257-286, 1992.

B. Courcelle, J. Engelfriet, and G. Rozenberg, Contex-free handle-rewriting hypergraph grammars. Graph-Grammars and Their Application to Computer Science, LNCS, vol.532, pp.253-268, 1991.

B. Courcelle and M. Mosbah, Monadic second-order evaluations on tree-decomposable graphs, Theoretical Computer Science, vol.109, issue.1-2, pp.49-82, 1993.
DOI : 10.1016/0304-3975(93)90064-Z

B. Courcelle and S. Olariu, Upper bounds to the clique width of graphs, Discrete Applied Mathematics, vol.101, issue.1-3, pp.77-114, 2000.
DOI : 10.1016/S0166-218X(99)00184-5

A. Cournier and M. Habib, A new linear algorithm for Modular Decomposition, Proceedings of Trees in Algebra and Programming -CAAP'94, pp.64-84, 1994.
DOI : 10.1007/BFb0017474

J. Díaz, J. Petit, and M. J. Serna, A survey of graph layout problems, ACM Computing Surveys, vol.34, issue.3, pp.313-356, 2002.
DOI : 10.1145/568522.568523

R. P. Dilworth, A Decomposition Theorem for Partially Ordered Sets, The Annals of Mathematics, vol.51, issue.1, pp.161-166, 1950.
DOI : 10.2307/1969503

G. A. Dirac, On rigid circuit graphs, Abhandlungen aus dem Mathematischen Seminar der Universit??t Hamburg, vol.13, issue.1-2, pp.71-76, 1961.
DOI : 10.1007/BF02992776

P. Duchon, N. Hanusse, E. Lebhar, and N. Schabanel, Could any graph be turned into a smallworld? Theor, Comput. Sci, vol.355, issue.1, pp.96-103, 2006.

J. A. Ellis and M. Markov, Computing the vertex separation of unicyclic graphs, Information and Computation, vol.192, issue.2, pp.123-161, 2004.
DOI : 10.1016/j.ic.2004.03.005

J. A. Ellis, I. H. Sudborough, and J. S. Turner, The Vertex Separation and Search Number of a Graph, Information and Computation, vol.113, issue.1, pp.50-79, 1994.
DOI : 10.1006/inco.1994.1064

S. P. Fekete and J. Schepers, A Combinatorial Characterization of Higher-Dimensional Orthogonal Packing, Mathematics of Operations Research, vol.29, issue.2, pp.353-368, 2004.
DOI : 10.1287/moor.1030.0079

F. V. Fomin, Searching expenditure and interval graphs, Discrete Applied Mathematics, vol.135, issue.1-3, pp.97-104, 2004.
DOI : 10.1016/S0166-218X(02)00297-4

F. V. Fomin, Helicopter search problems, bandwidth and pathwidth, Discrete Applied Mathematics, vol.85, issue.1, pp.59-70, 1998.
DOI : 10.1016/S0166-218X(97)00131-5

F. V. Fomin and P. A. Golovach, Graph Searching and Interval Completion, SIAM Journal on Discrete Mathematics, vol.13, issue.4, pp.454-464, 2000.
DOI : 10.1137/S0895480199350477

F. V. Fomin, P. Fraigniaud, and N. Nisse, Nondeterministic Graph Searching: From Pathwidth to Treewidth, Proceedings of MFCS 2005, pp.364-375, 2005.
URL : https://hal.archives-ouvertes.fr/hal-00421420

F. V. Fomin, P. Heggernes, and J. A. Telle, Graph Searching, Elimination Trees, and a Generalization of Bandwidth, Algorithmica, vol.41, issue.2, pp.73-87, 2004.
DOI : 10.1007/s00453-004-1117-y

F. V. Fomin, D. Kratsch, and H. Mller, On the domination search number, Discrete Applied Mathematics, vol.127, issue.3, pp.565-580, 2003.
DOI : 10.1016/S0166-218X(02)00389-X

F. V. Fomin, D. Kratsch, and I. Todinca, Exact (Exponential) Algorithms for Treewidth and Minimum Fill-In, Proceedings of ICALP 2004, pp.568-580, 2004.
DOI : 10.1007/978-3-540-27836-8_49

URL : https://hal.archives-ouvertes.fr/hal-00085561

F. Fomin and D. Thilikos, A 3-approximation for the pathwidth of Halin graphs

P. Fraigniaud, Greedy Routing in Tree-Decomposed Graphs, Proceedings of ESA 2005, pp.791-802, 2005.
DOI : 10.1007/11561071_70

P. Fraigniaud and N. Nisse, Connected Treewidth and Connected Graph Searching, Proceedings of LATIN 2006, pp.479-490, 2006.
DOI : 10.1007/11682462_45

URL : https://hal.archives-ouvertes.fr/inria-00423448

M. K. Franklin, Z. Galil, and M. Yung, Eavesdropping games: a graph-theoretic approach to privacy in distributed systems, Journal of the ACM, vol.47, issue.2, pp.225-243, 2000.
DOI : 10.1145/333979.333980

D. R. Fulkerson and O. A. , Incidence matrices and interval graphs, Pacific Journal of Mathematics, vol.15, issue.3, pp.835-855, 1965.
DOI : 10.2140/pjm.1965.15.835

T. Gallai, Transitiv orientierbare Graphen, Acta Mathematica Academiae Scientiarum Hungaricae, vol.51, issue.1-2, pp.25-66, 1967.
DOI : 10.1007/BF02020961

M. R. Garey and D. S. Johnson, Computer and Intractability: A Guide to the Theory of NP-Completeness, 1979.

F. Gavril, The intersection graphs of subtrees in trees are exactly the chordal graphs, Journal of Combinatorial Theory, Series B, vol.16, issue.1, pp.47-56, 1974.
DOI : 10.1016/0095-8956(74)90094-X

J. A. George and J. W. Liu, Computer Solution of Large Sparse Positive Definite Systems, 1981.

P. C. Gilmore and A. J. Hoffman, A characterization of comparability graphs and of interval graphs, Journal canadien de math??matiques, vol.16, issue.0, pp.539-548, 1964.
DOI : 10.4153/CJM-1964-055-5

P. W. Goldberg, M. C. Golumbic, H. Kaplan, and R. Shamir, Four Strikes Against Physical Mapping of DNA, Journal of Computational Biology, vol.2, issue.1, pp.139-152, 1995.
DOI : 10.1089/cmb.1995.2.139

M. C. Golumbic, Algorithmic Graph Theory and Perfect Graphs, 1984.

J. Gustedt, On the pathwidth of chordal graphs, Discrete Applied Mathematics, vol.45, issue.3, pp.233-248, 2003.
DOI : 10.1016/0166-218X(93)90012-D

URL : https://hal.archives-ouvertes.fr/inria-00549556

G. Gutin, S. Szeider, and A. Yeo, Fixed-Parameter Complexity of Minimum Profile Problems, Proceedings of IWPEC 2006, p.4169, 2006.

M. Habib, R. M. Mcconnell, C. Paul, and L. Viennot, Lex-BFS and partition refinement, with applications to transitive orientation, interval graph recognition and consecutive ones testing, Theoretical Computer Science, vol.234, issue.1-2, pp.59-84, 2000.
DOI : 10.1016/S0304-3975(97)00241-7

M. Habib and R. Moehring, Treewidth of cocomparability graphs and a new order-theoretic parameter, Order, vol.88, issue.3, pp.47-60, 1994.
DOI : 10.1007/BF01462229

M. Habib, C. Paul, and L. Viennot, PARTITION REFINEMENT TECHNIQUES: AN INTERESTING ALGORITHMIC TOOL KIT, International Journal of Foundations of Computer Science, vol.10, issue.02, pp.147-170, 1999.
DOI : 10.1142/S0129054199000125

T. Hagerup, Dynamic algorithms for graphs of bounded treewidth, Proceedings of ICALP 1997, pp.292-302, 1997.

P. Heggernes, Minimal triangulations of graphs: A survey, Discrete Mathematics, vol.306, issue.3, pp.297-317, 2006.
DOI : 10.1016/j.disc.2005.12.003

P. Heggernes and F. Mancini, Minimal Split Completions of Graphs, Proceedings of LATIN 2006, pp.592-604, 2006.
DOI : 10.1007/11682462_55

P. Heggernes, F. Mancini, and C. Papadopoulos, Minimal Comparability Completions, 2006.

P. Heggernes, K. Suchan, I. Todinca, and Y. Villanger, Characterizing Minimal Interval Completions, 2006.
DOI : 10.1007/978-3-540-70918-3_21

URL : https://hal.archives-ouvertes.fr/hal-00462305

P. Heggernes, J. A. Telle, and Y. Villanger, Computing minimal triangulations in time O(n ? logn) = o(n 2.376 ), Proceedings of the 16th Annual ACM-SIAM Symposium on Discrete Algorithms -SODA 2005, SIAM, pp.907-916, 2005.

C. Van-hoesel, A. Koster, and A. Kolen, Optimal solutions for a frequency assignement problem via tree-decomposition, Proceedings of WG, pp.338-349, 1999.

L. Ibarra, The clique-separator graph for chordal graphs and subclasses of chordal graphs, Presented at Symposium on Discrete Mathematics, 2004.

P. Jégou, S. Ndiaye, and C. Terrioux, Computing and Exploiting Tree-Decompositions for Solving Constraint Networks, Proceedings of CP 1995, pp.777-781, 2005.
DOI : 10.1007/11564751_63

P. Jégou and C. Terrioux, Hybrid backtracking bounded by tree-decomposition of constraint networks, Artificial Intelligence, vol.146, issue.1, pp.43-75, 2003.
DOI : 10.1016/S0004-3702(02)00400-9

H. Kaplan and R. Shamir, Pathwidth, Bandwidth, and Completion Problems to Proper Interval Graphs with Small Cliques, SIAM Journal on Computing, vol.25, issue.3, pp.540-561, 1996.
DOI : 10.1137/S0097539793258143

H. Kaplan, R. Shamir, and R. E. Tarjan, Tractability of Parameterized Completion Problems on Chordal, Strongly Chordal, and Proper Interval Graphs, SIAM Journal on Computing, vol.28, issue.5, pp.1906-1922, 1999.
DOI : 10.1137/S0097539796303044

M. Kiriousis and C. Papadimitriou, Searching and pebbling, Theoretical Computer Science, vol.47, issue.2, pp.205-218, 1986.
DOI : 10.1016/0304-3975(86)90146-5

D. J. Kleitman and R. Vohra, Computing the Bandwidth of Interval Graphs, SIAM Journal on Discrete Mathematics, vol.3, issue.3, pp.373-375, 1990.
DOI : 10.1137/0403033

T. Kloks, TREEWIDTH OF CIRCLE GRAPHS, International Journal of Foundations of Computer Science, vol.07, issue.02, pp.111-120, 1996.
DOI : 10.1142/S0129054196000099

T. Kloks and D. Kratsch, Treewidth of Chordal Bipartite Graphs, Journal of Algorithms, vol.19, issue.2, pp.266-281, 1995.
DOI : 10.1006/jagm.1995.1037

T. Kloks, D. Kratsch, and J. Spinrad, On treewidth and minimum fill-in of asteroidal triple-free graphs, Theoretical Computer Science, vol.175, issue.2, pp.309-335, 1997.
DOI : 10.1016/S0304-3975(96)00206-X

T. Kloks, D. Kratsch, and C. K. Wong, Minimum Fill-in on Circle and Circular-Arc Graphs, Journal of Algorithms, vol.28, issue.2, pp.272-289, 1998.
DOI : 10.1006/jagm.1998.0936

D. Kratsch and J. P. Spinrad, Between O(nm) and O(n ? ) Proceedings of SODA, pp.709-716, 2003.

D. Kratsch and J. Spinrad, Minimal fill in <mml:math altimg="si1.gif" overflow="scroll" xmlns:xocs="http://www.elsevier.com/xml/xocs/dtd" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.elsevier.com/xml/ja/dtd" xmlns:ja="http://www.elsevier.com/xml/ja/dtd" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:tb="http://www.elsevier.com/xml/common/table/dtd" xmlns:sb="http://www.elsevier.com/xml/common/struct-bib/dtd" xmlns:ce="http://www.elsevier.com/xml/common/dtd" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:cals="http://www.elsevier.com/xml/common/cals/dtd"><mml:mi mathvariant="normal">O</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msup><mml:mrow><mml:mi>n</mml:mi></mml:mrow><mml:mrow><mml:mn>2.69</mml:mn></mml:mrow></mml:msup><mml:mo stretchy="false">)</mml:mo></mml:math> time, Discrete Mathematics, vol.306, issue.3, pp.366-371, 2006.
DOI : 10.1016/j.disc.2005.12.009

A. Liotta, G. Pavlou, and G. Knight, Exploiting agent mobility for large-scale network monitoring, IEEE Network, vol.16, issue.3, pp.7-15, 2002.
DOI : 10.1109/MNET.2002.1002994

R. M. Mcconnell, Linear-Time Recognition of Circular-Arc Graphs, Algorithmica, vol.37, issue.2, pp.93-147, 2003.
DOI : 10.1007/s00453-003-1032-7

N. Meggido, S. L. Hakimi, M. R. Garey, D. S. Johson, and C. H. Papadimitriou, The complexity of searching a graph, Journal of the ACM, vol.35, issue.1, pp.18-44, 1988.
DOI : 10.1145/42267.42268

R. H. Mohring, D. Wagner, and F. Wagner, VLSI network design, a survey, Handbooks in Operations Research/Management Science, Volume on Networks, pp.625-712, 1995.

B. Monien, The Bandwidth Minimization Problem for Caterpillars with Hair Length 3 is NP-Complete, SIAM Journal on Algebraic Discrete Methods, vol.7, issue.4, pp.505-512, 1986.
DOI : 10.1137/0607057

A. Natanzon, R. Shamir, and R. Sharan, A Polynomial Approximation Algorithm for the Minimum Fill-In Problem, SIAM Journal on Computing, vol.30, issue.4, pp.1067-1079, 2000.
DOI : 10.1137/S0097539798336073

A. Natanzon, R. Shamir, and R. Sharan, Complexity classification of some edge modification problems, Discrete Applied Mathematics, vol.113, issue.1, pp.109-128, 2001.
DOI : 10.1016/S0166-218X(00)00391-7

S. Olariu, An optimal greedy heuristic to color interval graphs, Information Processing Letters, vol.37, issue.1, pp.21-25, 1991.
DOI : 10.1016/0020-0190(91)90245-D

B. S. Panda and S. K. Das, A linear time recognition algorithm for proper interval graphs, Information Processing Letters, vol.87, issue.3, pp.153-161, 2003.
DOI : 10.1016/S0020-0190(03)00298-9

A. Parra and P. Scheffler, Characterizations and algorithmic applications of chordal graph embeddings, Discrete Applied Mathematics, vol.79, issue.1-3, pp.171-188, 1997.
DOI : 10.1016/S0166-218X(97)00041-3

B. W. Peyton, Minimal Orderings Revisited, SIAM Journal on Matrix Analysis and Applications, vol.23, issue.1, pp.271-294, 2001.
DOI : 10.1137/S089547989936443X

I. Rappaport, K. Suchan, and I. Todinca, Minimal proper interval completions, Proceedings of WG 2006, 2006.

S. Rayan, R. Pradeep, and N. Paramesh, Network management platform based on mobile agents, International Journal of Network Management, vol.14, pp.59-73, 2004.

N. Robertson and P. D. Seymour, Graph minors. I. Excluding a forest, Journal of Combinatorial Theory, Series B, vol.35, issue.1, pp.39-61, 1983.
DOI : 10.1016/0095-8956(83)90079-5

N. Robertson and P. D. Seymour, Graph minors. II. Algorithmic aspects of tree-width, Journal of Algorithms, vol.7, issue.3, pp.309-322, 1986.
DOI : 10.1016/0196-6774(86)90023-4

URL : http://doi.org/10.1006/jctb.1999.1919

N. Robertson and P. D. Seymour, Graph minors. III. Planar tree-width, Journal of Combinatorial Theory, Series B, vol.36, issue.1, pp.49-64, 1984.
DOI : 10.1016/0095-8956(84)90013-3

URL : http://doi.org/10.1006/jctb.1999.1919

D. J. Rose, On simple characterizations of k-trees, Discrete Mathematics, vol.7, issue.3-4, pp.317-322, 1974.
DOI : 10.1016/0012-365X(74)90042-9

D. Rose, R. E. Tarjan, and G. Lueker, Algorithmic Aspects of Vertex Elimination on Graphs, SIAM Journal on Computing, vol.5, issue.2, pp.146-160, 1976.
DOI : 10.1137/0205021

P. Seymour and R. Thomas, Graph Searching and a Min-Max Theorem for Tree-Width, Journal of Combinatorial Theory, Series B, vol.58, issue.1, pp.22-33, 1993.
DOI : 10.1006/jctb.1993.1027

K. Skodinis, Construction of linear tree-layouts which are optimal with respect to vertex separation in linear time, Journal of Algorithms, vol.47, issue.1, pp.40-59, 2003.
DOI : 10.1016/S0196-6774(02)00225-0

K. Suchan and I. Todinca, Minimal interval completion through graph exploration, Proceedings of ISAAC 2006, 2006.
URL : https://hal.archives-ouvertes.fr/hal-00462293

K. Suchan and I. Todinca, Pathwidth of Circular-Arc Graphs, 2006.
DOI : 10.1007/978-3-540-74839-7_25

URL : https://hal.archives-ouvertes.fr/hal-00462302

R. Sundaram, K. S. Singh, and C. , Treewidth of Circular-Arc Graphs, SIAM Journal on Discrete Mathematics, vol.7, issue.4, pp.647-655, 1994.
DOI : 10.1137/S0895480191193789

E. Szpilrajn-marczewski, Sur deux propriétés des classes d'ensembles, Fundamenta Mathematicae, vol.33, pp.303-307, 1945.

E. Wanke, k-NLC graphs and polynomial algorithms, Discrete Applied Mathematics, vol.54, issue.2-3, pp.251-266, 1994.
DOI : 10.1016/0166-218X(94)90026-4

M. Yannakakis, Edge-Deletion Problems, SIAM Journal on Computing, vol.10, issue.2, pp.310-327, 1981.
DOI : 10.1137/0210021

M. Yannakakis, Computing the Minimum Fill-In is NP-Complete, SIAM Journal on Algebraic Discrete Methods, vol.2, issue.1, pp.77-79, 1981.
DOI : 10.1137/0602010