Rigid Reachability

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 P-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.

• Type: Conference
• Year: 1998
• Where: ASIAN
• Authors: Harald Ganzinger, Florent Jacquemard, Margus Veanes
• Keywords: Algorithms, ASIAN 1998, Certain Decidable Subclasses, Monadic Rigid Reachability, Rigid Reachability