# Publications in 2009

## 2009

- From Outermost to Context-Sensitive RewritingJörg Endrullis, and Dimitri HendriksIn: Proc. Conf. on Rewriting Techniques and Applications (RTA 2009), pp. 305–319, Springer (2009)paper
# Summary

We define a transformation from term rewriting systems (TRSs) to context-sensitive TRSs in such a way that termination of the target system implies outermost termination of the original system. For the class of left-linear TRSs the transformation is complete. Thereby state-of-the-art termination methods and automated termination provers for context-sensitive rewriting become available for proving termination of outermost rewriting. The translation has been implemented in Jambox, making it the most successful tool in the category of outermost rewriting of the last edition of the annual termination competition.

An extended version of this paper is available from Transforming Outermost into Context-Sensitive Rewriting (Logical Methods in Computer Science 2010).

See research for an overview of my research on termination.

# Bibtex

@inproceedings{termination:outermost:2009, author = {Endrullis, J\"{o}rg and Hendriks, Dimitri}, title = {{From Outermost to Context-Sensitive Rewriting}}, booktitle = {Proc.\ Conf.\ on Rewriting Techniques and Applications (RTA~2009)}, volume = {5595}, pages = {305--319}, publisher = {Springer}, series = {LNCS}, year = {2009}, doi = {10.1007/978-3-642-02348-4\_22}, keywords = {rewriting, termination, automata}, type = {conference} }

# Digital Object Identifier

10.1007/978-3-642-02348-4_22

- Local TerminationJörg Endrullis, Roel C. de Vrijer, and Johannes WaldmannIn: Proc. Conf. on Rewriting Techniques and Applications (RTA 2009), pp. 270–284, Springer (2009)paper
# Bibtex

@inproceedings{termination:local:2009, author = {Endrullis, J\"{o}rg and de~Vrijer, Roel C. and Waldmann, Johannes}, title = {{Local Termination}}, booktitle = {Proc.\ Conf.\ on Rewriting Techniques and Applications (RTA~2009)}, volume = {5595}, pages = {270--284}, publisher = {Springer}, series = {LNCS}, year = {2009}, doi = {10.1007/978-3-642-02348-4\_19}, keywords = {rewriting, termination, automata}, type = {conference} }

# Digital Object Identifier

10.1007/978-3-642-02348-4_19

- Complexity of Fractran and ProductivityJörg Endrullis, Clemens Grabmayer, and Dimitri HendriksIn: Proc. Conf. on Automated Deduction (CADE 2009), pp. 371–387, Springer (2009)paper
# Bibtex

@inproceedings{complexity:productivity:2009, author = {Endrullis, J\"{o}rg and Grabmayer, Clemens and Hendriks, Dimitri}, title = {{Complexity of Fractran and Productivity}}, booktitle = {Proc.\ Conf.\ on Automated Deduction (CADE~2009)}, volume = {5663}, pages = {371--387}, publisher = {Springer}, series = {LNCS}, year = {2009}, doi = {10.1007/978-3-642-02959-2\_28}, keywords = {rewriting, undecidability, productivity}, type = {conference} }

# Digital Object Identifier

10.1007/978-3-642-02959-2_28

- Degrees of Undecidability in Term RewritingJörg Endrullis, Herman Geuvers, and Hans ZantemaIn: Proc. Conf. on Computer Science Logic (CSL 2009), pp. 255–270, Springer (2009)paper
# Summary

Undecidability of various properties of first-order term rewriting systems is well-known. An undecidable property can be classified by the complexity of the formula defining it. This classification gives rise to a hierarchy of distinct levels of undecidability, starting from the arithmetical hierarchy classifying properties using first order arithmetical formulas, and continuing into the analytic hierarchy, where quantification over function variables is allowed.

In this paper we give an overview of how the main properties of first-order term rewriting systems are classified in these hierarchies. We consider properties related to normalization (strong normalization, weak normalization and dependency problems) and properties related to confluence (confluence, local confluence and the unique normal form property). For all of these we distinguish between the single term version and the uniform version. Where appropriate, we also distinguish between ground and open terms.

Most uniform properties are \( \Pi^0_2 \)-complete. The particular problem of local confluence turns out to be \( \Pi^0_2 \)-complete for ground terms, but only \( \Sigma^0_1 \)-complete (and thereby recursively enumerable) for open terms. The most surprising result concerns dependency pair problems without minimality flag: we prove this problem to be \( \Pi^1_1 \)-complete, hence not in the arithmetical hierarchy, but properly in the analytic hierarchy.

We refer to

*Levels of Undecidability in Rewriting*(Information and Computation 2011) for an extended journal version of this paper.# Bibtex

@inproceedings{rewriting:undecidability:degrees:2009, author = {Endrullis, J\"{o}rg and Geuvers, Herman and Zantema, Hans}, title = {{Degrees of Undecidability in Term Rewriting}}, booktitle = {Proc.\ Conf.\ on Computer Science Logic (CSL~2009)}, volume = {5771}, pages = {255--270}, publisher = {Springer}, series = {LNCS}, year = {2009}, doi = {10.1007/978-3-642-04027-6\_20}, keywords = {rewriting, undecidability, termination, confluence}, type = {conference} }

# Digital Object Identifier

10.1007/978-3-642-04027-6_20