Algebraic laws for nondeterminism and concurrency
Journal of the ACM (JACM)
Journal of the ACM (JACM) - The MIT Press scientific computation series
Three partition refinement algorithms
SIAM Journal on Computing
CCS expressions finite state processes, and three problems of equivalence
Information and Computation
Process algebra
On the regular structure of prefix rewriting
CAAP '90 Selected papers of the conference on Fifteenth colloquium on trees in algebra and programming
Decidability of bisimulation equivalence for process generating context-free languages
Journal of the ACM (JACM)
Undecidability of bisimilarity for Petri nets and some related problems
STACS '94 Selected papers of the eleventh symposium on Theoretical aspects of computer science
Bisimulation equivalence is decidable for all context-free processes
Information and Computation
A polynomial algorithm for deciding bisimilarity of normed context-free processes
Theoretical Computer Science
Decidability of bisimulation equivalence for normed pushdown processes
Theoretical Computer Science
Information and Computation - Special issue on EXPRESS 1997
L(A) = L(B)? decidability results from complete formal systems
Theoretical Computer Science
Decidability of DPDA equivalence
Theoretical Computer Science
Introduction to the Theory of Computation
Introduction to the Theory of Computation
Communication and Concurrency
An Elementary Bisimulation Decision Procedure for Arbitrary Context-Free Processes
MFCS '95 Proceedings of the 20th International Symposium on Mathematical Foundations of Computer Science
On the Complexity of Semantic Equivalences for Pushdown Automata and BPA
MFCS '02 Proceedings of the 27th International Symposium on Mathematical Foundations of Computer Science
Strong Bisimilarity and Regularity of Basic Process Algebra Is PSPACE-Hard
ICALP '02 Proceedings of the 29th International Colloquium on Automata, Languages and Programming
On Infinite Transition Graphs Having a Decidable Monadic Theory
ICALP '96 Proceedings of the 23rd International Colloquium on Automata, Languages and Programming
On the Ehrenfeucht-Fraïssé Game in Theoretical Computer Science
TAPSOFT '93 Proceedings of the International Joint Conference CAAP/FASE on Theory and Practice of Software Development
High Undecidability of Weak Bisimilarity for Petri Nets
TAPSOFT '95 Proceedings of the 6th International Joint Conference CAAP/FASE on Theory and Practice of Software Development
Reachability Analysis of Pushdown Automata: Application to Model-Checking
CONCUR '97 Proceedings of the 8th International Conference on Concurrency Theory
Decidability of Bisimulation Equivalence for Normed Pushdown Processes
CONCUR '96 Proceedings of the 7th International Conference on Concurrency Theory
CONCUR '96 Proceedings of the 7th International Conference on Concurrency Theory
Concurrency and Automata on Infinite Sequences
Proceedings of the 5th GI-Conference on Theoretical Computer Science
Efficient Algorithms for Model Checking Pushdown Systems
CAV '00 Proceedings of the 12th International Conference on Computer Aided Verification
CONCUR '95 Proceedings of the 6th International Conference on Concurrency Theory
Decidability of Bisimulation Equivalence for Equational Graphs of Finite Out-Degree
FOCS '98 Proceedings of the 39th Annual Symposium on Foundations of Computer Science
Bisimulation and language equivalence
Logic for concurrency and synchronisation
The Bisimulation Problem for Equational Graphs of Finite Out-Degree
SIAM Journal on Computing
Equivalence-checking on infinite-state systems: Techniques and results
Theory and Practice of Logic Programming
Selected Ideas Used for Decidability and Undecidability of Bisimilarity
DLT '08 Proceedings of the 12th international conference on Developments in Language Theory
Information and Computation
Decidability of behavioral equivalences in process calculi with name scoping
FSEN'11 Proceedings of the 4th IPM international conference on Fundamentals of Software Engineering
BPA bisimilarity is EXPTIME-hard
Information Processing Letters
Bisimilarity of Pushdown Automata is Nonelementary
LICS '13 Proceedings of the 2013 28th Annual ACM/IEEE Symposium on Logic in Computer Science
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Stirling [1996, 1998] proved the decidability of bisimilarity on so-called normed pushdown processes. This result was substantially extended by Sénizergues [1998, 2005] who showed the decidability of bisimilarity for regular (or equational) graphs of finite out-degree; this essentially coincides with weak bisimilarity of processes generated by (unnormed) pushdown automata where the ϵ-transitions can only deterministically pop the stack. The question of decidability of bisimilarity for the more general class of so called Type -1 systems, which is equivalent to weak bisimilarity on unrestricted ϵ-popping pushdown processes, was left open. This was repeatedly indicated by both Stirling and Sénizergues. Here we answer the question negatively, that is, we show the undecidability of bisimilarity on Type -1 systems, even in the normed case. We achieve the result by applying a technique we call Defender's Forcing, referring to the bisimulation games. The idea is simple, yet powerful. We demonstrate its versatility by deriving further results in a uniform way. First, we classify several versions of the undecidable problems for prefix rewrite systems (or pushdown automata) as Π01-complete or Σ11-complete. Second, we solve the decidability question for weak bisimilarity on PA (Process Algebra) processes, showing that the problem is undecidable and even Σ11-complete. Third, we show Σ11-completeness of weak bisimilarity for so-called parallel pushdown (or multiset) automata, a subclass of (labeled, place/transition) Petri nets.