Publications Walter J. Gutjahr:
Fair and efficient vaccine allocation: a generalized Gini index approach,
Walter J. Gutjahr,
Production and Operations Management 32 (12), pp. 4114-4134 (2023).
Risk-averse bargaining in a stochastic optimization context,
Walter J. Gutjahr, Raimund Kovacevic, David Wozabal,
Manufacturing & Service Operations Management 25 (1), pp. 323-340 (2023).
Bi-objective risk-averse facility location using a subset-based representation of the conditional value-at-risk,
Najmesadat Nazemi, Sophie N. Parragh, Walter J. Gutjahr,
Proc. ICORES 2022, pp. 77-85 (2022).
Bi-objective facility location under uncertainty with an application in last-mile disaster relief,
Najmesadat Nazemi, Sophie N. Parragh, Walter J. Gutjahr,
Annals of Operations Research 319, pp. 1689-1716 (2022).
Stochastic radiotherapy appointment scheduling,
Roland Braune, Walter J. Gutjahr, Petra Vogl,
Central European Journal of Operations Research 30, pp. 1239-1277 (2022).
A branch-and-Benders-cut algorithm for a bi-objective stochastic facility location problem,
Sophie N. Parragh, Fabien Tricoire, Walter J. Gutjahr,
OR Spectrum 44, pp. 419-459 (2022).
Stochastic premarshalling of block stacking warehouses,
Vittorio Maniezzo, Marco A. Boschetti, Walter J. Gutjahr,
Omega 102, 102336 (2021).
Inequity-averse stochastic decision processes,
European Journal of Operational Research 288, pp. 258-270 (2021).
Preprint
Innovative approaches in humanitarian operations (Editorial),
with: N. Noyan, N. Vandaele, L. Van Wassenhove,
OR Spectrum 42, pp. 585-589 (2020).
Stochastic project management: multiple projects with multi-skilled human resources,
with: Th. Felberbauer, K.F. Doerner,
Journal of Scheduling 22, pp. 271-288 (2019).
Inequity-averse shelter location for disaster preparedness,
with: M. Mostajabdaveh, F.S. Salman,
IISE Transactions 51, pp. 809-829 (2019).
Stochastic search in metaheuristics,
with: R. Montemanni,
in: Handbook of Metaheuristics: Third Edition, eds.: Gendreau, M., Potvin, J.-Y.,
Springer, pp. 513--540 (2019).
Equity and deprivation costs in humanitarian logistics,
with: S. Fischer,
European J. of Operational Research 270, pp. 185-197 (2018).
A dynamic simulation-optimization approach for managing mass casualty incidents,
with: H. Niessner, M. Rauner,
Operations Research for Health Care 17, pp. 82-100 (2018).
Sampling-based genetic algorithms for the bi-objective stochastic covering tour problem,
with: M. Zehetner,
Recent Developments in Metaheuristics, eds.: Amodeo, L., Talbi, E.-G., Yalaoui, F., Springer, pp. 253-284 (2018).
Efficient pairwise preference elicitation allowing for indifference,
with: J. Branke, S. Corrente, S. Greco,
Computers and Operations Research 88, pp. 175-186 (2017).
Modelling beneficiaries' choice in disaster relief logistics,
with: Ch. Burkart, P.C. Nolz,
Annals of Operations Research 256, pp. 41-61 (2017).
Hybrid metaheuristics for project scheduling and staffing considering interruptions between project periods and labor contracts,
with: T. Felberbauer, K.F. Doerner,
Dynamic Perspectives on Managerial Decision Making, eds. Dawid, H., Doerner, K.F., Feichtinger, G., Kort, P., Seidl, A., pp. 349-377 (2016).
Stochastic real world warehouse premarshalling,
with: V. Maniezzo, M. Boschetti,
Proc. Matheuristics 2016, pp. 100-103 (2016).
Bi-objective stochastic programming models for determining depot locations in disaster relief operations,
with: S. Rath, M. Gendreau,
International Transactions in Operational Research 23, pp. 997-1023 (2016).
Multicriteria optimization in humanitarian aid,
with: P.C. Nolz,
European J. of Operational Research 252, pp. 351-366 (2016).
Bi-objective bilevel optimization of distribution center locations considering user equilibria,
with: N. Dzubur,
Transportation Research Part E 85, pp. 1-22 (2016).
Stochastic multi-objective optimization: a survey on non-scalarizing methods,
with: A. Pichler,
Annals of Operations Research 236, pp. 475-499 (2016).
Bi-objective multi-mode project scheduling under risk aversion,
European J. of Operational Research 246, pp. 421-434 (2015).
Using indifference information in robust ordinal regression,
with: J. Branke, S. Greco, S. Corrente,
in: Evolutionary Multi-Criterion Optimization, Springer International Publishing, pp. 205-217 (2015).
Project portfolio selection under skill development,
in: Handbook on Project Management and Scheduling Vol. 2 (eds.: Christoph Schwindt and Juergen Zimmermann),
Springer International Publishing, pp. 729-750 (2015).
A three-objective optimization approach to cost effectiveness analysis under uncertainty,
Operations Research Proceedings 2012 (Selected Papers of the Int. Annual
Conf. of the German Operations Research Society,
Hannover, Germany, Sept. 5-7, 2012),
eds.: Stefan Helber et al., Springer, pp. 239-246 (2014).
A math-heuristic for the warehouse location routing problem in disaster relief,
with: S. Rath,
Computers and Operations Research 42, pp. 25-39 (2014).
Project portfolio selection under uncertainty with outsourcing opportunities,
with: K.A. Froeschl,
Flexible Services and Manufacturing Journal 25, pp. 255-281 (2013).
Runtime analysis of an evolutionary algorithm for stochastic multi-objective combinatorial optimization,
Evolutionary Computation 20, pp. 395-421 (2012).
Preprint
Exact hybrid algorithms for solving a bi-objective vehicle routing problem,
with: P. Reiter,
Central European Journal of Operations Research 20, pp. 19-43 (2012).
Training on the project: a quantifying approach to competence development,
with: K.A. Froeschl, M. Denk, H. Riedmann, C. Stummer,
Knowledge Management Research and Practice 10, pp. 64-78 (2012).
The bi-objective stochastic covering tour problem,
with: F. Tricoire, A. Graf,
Computers and Operations Research 39, pp. 1582-1592 (2012).
Preprint
A note on the utility-theoretic justification of the Pareto approach in
stochastic multi-objective combinatorial optimization,
Proc. 11th Internat. Symposium on Operational Research in Slovenia (SOR '11),
Dolenjske Toplice, Slovenia, Sept. 28-30, 2011,
eds.: L. Zadnik Stirn, J. Zerovnik, J. Povh, S. Drobne, A. Lisec, pp. 7-12 (2011).
Optimization in disaster relief (Editorial),
with: K.F. Doerner, L. Van Wassenhove,
OR Spectrum 33, pp. 445-449 (2011).
Recent trends in metaheuristics for stochastic combinatorial optimization,
Central European Journal of Computer Science 1, pp. 58-66 (2011).
Optimal dynamic portfolio selection for projects under a competence development model,
OR Spectrum 33, pp. 173-206 (2011).
Ant colony optimization: recent developments in theoretical analysis,
in: Theory of Randomized Search Heuristics
(eds.: A. Auger, B. Doerr), World Scientific Publishing,
pp. 225-254 (2011).
Warehouse location routing problem for disaster relief,
with: S. Rath, K.F. Doerner,
Proc. MIC '09 (Metaheuristics International Conference), Hamburg, Germany, 13-16 July 2009, eds.: S. Voss, M. Caserta (2011).
Dynamic policy modeling for chronic diseases: metaheuristic-based identification of pareto-optimal screening strategies,
with: M. Rauner, K. Heidenberger, J. Wagner, J. Pasia,
Operations Research 58, pp. 1269-1286 (2010).
Stochastic search in metaheuristics,
in: Handbook of Metaheuristics, 2nd Edition (eds.: M. Gendreau, Y. Potvin),
Springer International Series in Operations Research and Management Science 146, pp. 573-597 (2010).
Bi-objective project portfolio selection and staff assignment under uncertainty,
with: P. Reiter,
Optimization: A Journal of Mathematical Programming and Operations Research 59, pp. 417-445 (2010).
Multi-objective decision analysis for competence-oriented project portfolio selection,
with: S. Katzensteiner, P. Reiter, C. Stummer, M. Denk,
European J. of Operational Research 205, pp. 670-679 (2010).
A bi-objective metaheuristic for disaster relief operation planning,
with: P.C. Nolz, K.F. Doerner, R.F. Hartl,
Advances in Multi-Objective Nature Inspired Computing (eds: C.A. Coello Coello, C. Dhaenes, L. Jourdan),
Springer Studies in Computational Intelligence 272, pp. 167-187 (2010).
Convergence analysis of metaheuristics,
Annals of Information Systems 10 (special issue on
"Matheuristics: Hybridizing Metaheuristics and Mathematical Programming",
eds.: V. Maniezzo, T. Stuetzle, S. Voss), pp. 159-187 (2009).
A multicriteria decision support system for competence-driven project portfolio selection,
with: C. Stummer, E. Kiesling,
International Journal of Information Technology and Decision Making 8, pp. 379-401 (2009).
Multi-criteria location planning for public facilities in tsunami-prone coastal areas,
with: K. Doerner, P. Nolz,
OR Spectrum 31, pp. 651-678 (2009).
A provably convergent heuristic for stochastic bicriteria integer programming,
Journal of Heuristics 15, pp. 227-258 (2009).
A survey on metaheuristics for stochastic combinatorial optimization,
with: L. Bianchi, M. Dorigo, L.M. Gambardella,
Natural Computing 8, pp. 239-287 (2009).
Stochastic local search procedures for the probabilistic two-days vehicle-routing problem,
with: K. Doerner, R. Hartl, G. Lulli,
in: Advances in Computational Intelligence in Transportation and Logistics, A. Fink, F. Rothlauf (eds.),
Springer: Berlin Heidelberg, Studies in Computational Intelligence 144, pp. 153-168 (2008).
Competence-driven project portfolio selection, scheduling and staff assignment,
with: S. Katzensteiner, P. Reiter, C. Stummer, M. Denk,
Central European J. of Operations Research 16, pp. 281-306 (2008).
(Download PDF)
Runtime analysis of ant colony optimization with best-so-far reinforcement,
with: G. Sebastiani,
Methodology and Computing in Applied Probability 10, pp. 409-433 (2008).
(Download PDF).
Search-based software engineering (Editorial),
with: M. Harman,
Computers and Operations Research 35 (no. 10), pp. 3049-3051 (2008).
(Download PDF)
Nature-inspired metaheuristics for multiobjective activity crashing,
with: K. Doerner, R.F. Hartl, C. Strauss, C. Stummer,
Omega 36, pp. 1019-1037 (2008).
(Download PDF)
First steps to the runtime complexity analysis of ant colony optimization,
Computers and Operations Research 35 (no. 9), pp. 2711-2727 (2008).
(Download PDF)
Mathematical runtime analysis of ACO algorithms: survey on an emerging issue,
Swarm Intelligence 1, pp. 59-79 (2007).
(Download PDF)
Multicriteria tour planning for mobile healthcare facilities in a developing country,
with: K. Doerner, A. Focke,
European J. of Operational Research 179 (no. 3), pp. 1078-1096 (2007).
(Download PDF)
Combined discrete-event simulation and ant colony optimisation approach for selecting optimal screening policies for diabetic retinopathy,
with: S.C. Brailsford, M. Rauner, W. Zeppelzauer,
Computational Management Science 4 (no. 1), pp. 59-83 (2007).
A VNS algorithm for noisy problems and its application to project portfolio analysis,
with: S. Katzensteiner, P. Reiter,
Proc. SAGA 2007 (Stochastic Algorithms: Foundations and Applications), eds.: J. Hromkovic et al.,
Springer Lecture Notes in Computer Science 4665, pp. 93-104 (2007).
(Download PDF)
An ACO algorithm for a dynamic regional nurse-scheduling problem in Austria,
with: M. Rauner,
Computer and Operations Research 34 (no. 3), pp. 642-666 (2007).
(Download PDF)
Enriched workflow modelling and stochastic branch-and-bound,
with: K. Doerner, G. Kotsis, M. Polaschek, C. Strauss,
European J. of Operational Research 75 (no. 3), pp. 1798-1817 (2006).
(Download PDF)
On the finite-time dynamics of ant colony optimization,
Methodology and Computing in Applied Probability 8, pp. 105-133 (2006).
(Download PDF)
Interaction dynamics of two reinforcement learners,
Central European J. of Operations Research 14, pp. 59-86 (2006).
(Download PDF)
Pareto Ant Colony Optimization with IP preprocessing in multiobjective project portfolio selection,
with: K. Doerner, R.F. Hartl, C. Strauss, C. Stummer,
European Journal of Operational Research 171, pp. 830-841 (2006).
(Download PDF)
Heuristic solution of an extended double-coverage ambulance location problem for Austria,
with: K. Doerner, R.F. Hartl, M. Karall, M. Reimann,
Central European J. of Operations Research 13, pp. 325-340 (2005).
(Download PDF)
Two metaheuristics for multiobjective stochastic combinatorial optimization,
Proc. SAGA 2005 (Stochastic Algorithms: Foundations and Applications),
Oct. 2005, Moscow (Russia), eds.: O.B. Lupanov, O.M. Kasim-Zade, A.V. Chaskin, K. Steinhoefl,
Springer Lecture Notes in Computer Science 3777, pp. 116-125 (2005).
(Download PDF)
Optimal screening policies for diabetic retinopathy using a combined discrete-event simulation and ant colony optimization approach,
with: M. Rauner, S.C. Brailsford, W. Zeppelzauer,
Proc. Int. Conference on Health Sciences Simulation, Western MultiConference '05,
eds.: Anderson, J.G., Katzper, M., pp. 147-152 (2005).
S-ACO: An ant-based approach to combinatorial optimization under uncertainty,
Proc. ANTS 2004 (4th International Workshop on Ant Colony Optimization and Swarm Intelligence, Brussels),
Springer LNCS 3172, pp. 238-249 (2004).
(Download PDF)
Chains, disks and drums: Ant Colony Optimization on diverse construction graphs,
Dagstuhl Seminar Extended Abstracts, Seminar "Theory of Evolutionary Algorithms",
International Conference and Research Center for Computer Science, Dagstuhl, Germany (2004).
Pareto Ant Colony Optimization: A metaheuristic approach to multiobjective portfolio selection,
with: K. Doerner, R.F. Hartl, C. Strauss, C. Stummer,
Annals of Operations Research 131, pp. 79-99 (2004).
(Download PDF)
A probabilistic two-day delivery vehicle routing problem,
with: K. Doerner, R.F. Hartl, G. Lulli,
Proc. TRISTAN 2004 (Triennial Symposium on Transportation Analysis, Guadeloupe), CD ROM (2004).
An Ant System approach to Markov decision processes,
with: H. S. Chang, J. Yang, S. Park,
Proc. American Control Conference 2004, pp. 3820-3825 (2004).
A generalized convergence result for the graph-based ant system metaheuristic,
Probability in the Engineering and Informational Sciences 17, pp. 545 - 569 (2003).
(Download PDF)
A converging ACO algorithm for stochastic combinatorial optimization,
Proc. SAGA 2003 (Stochastic Algorithms: Foundations and Applications),
Sept. 2003, Hatfield (UK), eds.: A. Albrecht, K. Steinhoefl,
Springer LNCS 2827, pp. 10 - 25 (2003).
(Download PDF)
Can simulation techniques contribute to microsociological theory? The case of learning matrices,
with: A. Eder,
Developments in Applied Statistics, Eds.: A. Ferligoj, A. Mrvar,
FDV: Ljubljana, pp. 219 - 242 (2003).
Scheduling multiprocessor tasks in presence of correlated failures,
with: I. Czarnowski, P. Jedrzejowicz, E. Ratajcak, A. Skakowski, I. Wierzbowska,
Central European J. of Operations Research 11, pp. 163 - 182 (2003).
(Download Postscript)
Extracting test sequences from a Markov software usage model by ACO,
with: K. Doerner,
Proc. GECCO 2003 (Genetic and Evolutionary Computation),
July 2003, Chicago (USA), Eds.: E. Cantu-Paz et al.,
Springer LNCS 2724, pp. 2465 - 2476 (2003).
(Download Postscript)
Using a reliability growth model to control software inspection,
with: S. Biffl,
Empirical Software Engineering 7, pp. 257 - 284 (2002).
ACO algorithms with guaranteed convergence to the optimal
solution,
Information Processing Letters 82, pp. 145 - 153 (2002).
(Download Postscript)
The move-to-partner rule for self-organizing task allocation
on a linear array,
Stochastic Models 18, No.1, pp. 109 - 137 (2002).
(Download Postscript)
A branch-and-bound approach to the optimization of redundant
software under failure correlation,
with: G. Uchida,
Computers and Operations Research 29, pp. 1773 - 1791 (2002).
(Download Postscript)
Investitionsentscheidungen bei mehrfachen Zielsetzungen und künstliche Ameisen,
with: K. Dörner, R.F. Hartl, Ch. Strauss, Ch. Stummer,
in: P. Chamoni, R. Leisten, A. Martin, J. Minnemann (Eds.),
Operations Research Proceedings 2001, Selected Papers of OR 2001,
Springer, Berlin, pp. 355-362 (2002).
Influence of team size and defect detection technique on inspection effectiveness,
with: S. Biffl,
Proc. METRICS 2001 (Software Metrics Symposium), pp. 63-75 (2001).
A reliability model for nonhomogeneous redundant software version with
correlated failures,
Computer Systems Science & Engineering 16 (no. 6), pp. 361 - 370 (2001).
(Download Postscript)
A Markov model for dyadic interaction learning,
with: A. Eder,
Proc. 5th European Workshop on Reinforcement Learning,
Utrecht, Sept. 2001, pp. 17 - 18 (2001).
Modelling social interactions by learning markovian matrices,
with: A. Eder, E. Neuwirth,
Proc. 8th International Facet Theory Conference,
Prague, July 2001, pp. 95 - 106 (2001).
Ant Colony Optimization in multiobjective portfolio selection,
with: K. Dörner, R. Hartl, Ch. Strauss,
Ch. Stummer,
Proc. MIC 2001 (4th Metaheuristics International Conference),
Porto (Portugal), July 2001, pp. 243 - 248 (2001).
Scheduling multiprocessor tasks in presence of correlated
failures,
with: I. Czarnowski, P. Jedrzejowicz, E. Ratajczak,
A. Skakowski, I. Wierzbowska,
Proc. SCASE 2001 (2nd International Workshop on Soft Computing Applied to Software
Engineering),
Enschede (Netherlands), Feb. 2001, pp. 67 - 77 (2001).
A stochastic branch-and-bound approach to activity crashing in
project management,
with: Ch. Strauss, E. Wagner,
INFORMS J. on Computing, vol. 12, pp. 125 - 135 (2000).
(Download Postscript)
Representation and optimization of software usage models with non-Markovian state
transitions,
with: K. Doerner,
Information and Software Technology, vol. 42, pp. 873 - 887 (2000).
(Download Postscript)
Software dependability evaluation based on Markov usage models,
Performance Evaluation, vol. 40, pp. 199 - 222 (2000).
(Download Postscript)
A graph-based Ant System and its convergence,
Future Generation Computer Systems, vol. 16, pp. 873 - 888 (2000).
(Download Postscript)
Crashing of stochastic processes by sampling and optimization,
with: Ch. Strauss, M. Toth,
Business Process Management Journal, vol. 6, pp. 65 - 84 (2000).
Partition testing versus random testing: the influence of uncertainty,
IEEE Transactions on Software Engineering, vol. 25, pp. 661 - 674 (1999).
(Download Postscript)
Optimal stochastic single-machine tardiness scheduling by stochastic branch-and-bound,
with: A. Hellmayr, G. Pflug,
European J. of Operational Research, vol. 117, pp. 396 - 413 (1999).
(Download Postscript)
Reliability optimization of redundant software with correlated failures,
Proc. ISSRE ' 98 (International Symposium on Software Reliability Engineering),
pp. 293 - 303, IEEE Computer Society (1998),
Best Paper Award ISSRE '98.
(Download Postscript)
Task assignment in Cayley interconnection topologies,
with: M. Hitz, T. Mück,
Parallel Computing,
vol. 23, pp. 1429 - 1460 (1997).
An improved algorithm for finding minimum-risk 3-state-device
networks,
with: Ch. Wöber,
International J. of Computer Mathematics, vol. 64, pp. 59 - 72 (1997).
Importance sampling of test cases in Markovian
software usage models,
Probability in the Engineering and Informational Sciences,
vol. 11, pp. 19 - 36 (1997).
(Download Postscript)
Failure risk estimation via Markov software usage models,
Proc. SAFECOMP ' 96 (International Conference on Computer Safety,
Reliability and Security),
pp. 183 - 192, Springer (1997).
(Download Postscript)
Risikogesteuerte Aufteilung von Softwaretestkapazitäten, in:
Test, Analyse und Verifikation von Software:
Aus der Arbeit der Fachgruppe 2.1.7 der Gesellschaft für Informatik
(ed. M. Müllerburg, A. Spillner, P. Liggesmeyer), pp. 197 - 211,
Oldenbourg (1996).
(Download Postscript)
Design of reliable 3-state-device networks by genetic algorithms
and simulated annealing,
Central European Journal of Operations Research and Economics,
vol. 3, pp. 257 - 284 (1996).
Simulated annealing for noisy cost functions,
with: G. Pflug,
J. of Global Optimization, vol. 8, pp. 1 - 13 (1996).
(Download Postscript)
Configurations of series-parallel networks with maximum reliability,
with: G. Pflug, A. Ruszczynski,
Microelectronics and Reliability, vol. 36, pp. 247 - 253 (1996).
Estimating qualifications in a self-evaluating group,
with: I. Bomze,
Quality and Quantity, vol. 29, pp. 241 - 250 (1995).
Paradoxien der Prognose und der Evaluation: Eine fixpunkttheoretische
Analyse,
Collegium Logicum - Annals of the Kurt Gödel Society, vol. 1,
pp. 54 - 66 (1995).
Optimal test distributions for software failure cost estimation,
IEEE Transactions on Software Engineering,
vol. 21, pp. 219 - 228 (1995).
(Download Postscript)
Efficient selection of test data from a polyhedral input domain,
with: G. Danninger,
Operations Research Proceedings 1994
(ed. U. Derigs, A. Bachem, A. Drexl),
pp. 233 - 238, Springer (1995).
Connection reliabilities in stochastic acyclic networks,
Random Structures and Algorithms, vol. 5, pp. 57 - 71 (1994).
The dynamics of self-evaluation,
with: I. Bomze,
Applied Mathematics and Computation, vol. 64, pp. 47 - 63 (1994).
Risikoorientiertes Software-Testen,
Softwaretechnik-Trends, Bd. 14, Heft 2, pp. 4 - 5 (1994).
Test point optimization in a branching-process-based reliability
model,
with: G. Danninger,
Probability in the Engineering and Informational
Sciences, vol. 8, pp. 591 - 609 (1994).
A global optimization problem in series-parallel networks with
maximum reliability,
J. of Global Optimization, vol. 5, pp. 403 - 404 (1994).
Expectation transfer between branching processes and random trees,
Random Structures and Algorithms, vol. 4, pp. 447 - 467 (1993).
Automatische Testdatengenerierung zur Unterstützung des
Softwaretests,
Informatik Forschung und Entwicklung, vol. 8, pp. 128 - 136 (1993).
Generating nonequivalent arithmetical expressions uniformly
at random,
Bayreuther Mathematische Schriften, vol. 43, pp. 1 - 10 (1993).
Average execution times of series-parallel networks,
with: G. Pflug,
Actes 29e Seminaire Lotharingien de Combinatoire,
pp. 35 - 41, Strasbourg: Publ. I.R.M.A. (1993).
The variance of level numbers in certain families of trees,
Random Structures and Algorithms,
vol. 3, pp. 361 - 374 (1992).
The asymptotic contour process of a binary tree is a
Brownian excursion,
with: G. Pflug,
Stochastic Processes and Applications, vol. 41, pp. 69 - 89 (1992).
The limiting common distribution of two leaf heights in a
random binary tree,
with: G. Pflug,
Theoretical Informatics and Applications,
vol. 26, pp. 1 - 18 (1992).
The asymptotic distribution of leaf heights in binary trees,
with: G. Pflug,
Graphs and Combinatorics, vol. 8, pp. 243 - 251 (1992).
Uniform random generation of expressions respecting algebraic
identities,
Computing, vol. 47, pp. 51 - 67 (1991).
Software-Testen mit Zufallsdaten: Eine Effizienzbewertung,
Zeitschrift für Statistik und Informatik, vol. 21,
pp. 57 - 70 (1991).
On the co-structure of k paths in a random binary tree,
J. of Combinatorial Mathematics and Combinatorial Computing,
vol. 10, pp. 105 - 117 (1991).
Enumeration of program structures as trees with commutative
or associative nodes,
J. of Combinatorics, Information and System Sciences,
vol. 12, pp. 13 - 24
(1987).
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