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Rigid reachability

Ganzinger, Harald and Jacquemard, Florent and Veanes, Margus

September 1998, 24 pages.

Status: available - back from printing

We show that rigid reachability, the non-symmetric form of rigid E-unification, is undecidable already in the case of a single constraint. From this we infer the undecidability of a new rather restricted kind of second-order unification. We also show that certain decidable subclasses of the problem which are PTIME-complete in the equational case become EXPTIME-complete when symmetry is absent. By applying automata-theoretic methods, simultaneous monadic rigid reachability with ground rules is shown to be in EXPTIME.

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  AUTHOR = {Ganzinger, Harald and Jacquemard, Florent and Veanes, Margus},
  TITLE = {Rigid reachability},
  TYPE = {Research Report},
  INSTITUTION = {Max-Planck-Institut f{\"u}r Informatik},
  ADDRESS = {Im Stadtwald, D-66123 Saarbr{\"u}cken, Germany},
  NUMBER = {MPI-I-98-2-013},
  MONTH = {September},
  YEAR = {1998},
  ISSN = {0946-011X},