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Checking NFA Equivalence with Bisimulations up to Congruence Filippo Bonchi and Damien Pous CNRS, LIP, ENS Lyon POPL, Roma, 25.1.2o13 Language equivalence of finite automata Useful for model checking: check that a program refines its


  1. Checking NFA Equivalence with Bisimulations up to Congruence Filippo Bonchi and Damien Pous CNRS, LIP, ENS Lyon POPL, Roma, 25.1.2o13

  2. Language equivalence of finite automata ◮ Useful for model checking: ◮ check that a program refines its specification ◮ compute a sequence A i of automata until A i ∼ A i +1 (cf. abstract regular model checking) ◮ Useful in proof assistants: ◮ decide the equational theory of Kleene algebra ( R ∪ S ) ⋆ = R ⋆ ; ( S ; R ⋆ ) ⋆ (cf. the ATBR and RelationAlgebra Coq libraries) ◮ This work: a new algorithm Filippo Bonchi & Damien Pous 2/26

  3. Outline Deterministic Automata Non-Deterministic Automata Comparison with other algorithms Filippo Bonchi & Damien Pous 3/26

  4. � � Checking language equivalence Deterministic case, first algorithm: a � z a � y x a a � v u a Filippo Bonchi & Damien Pous 4/26

  5. � � Checking language equivalence Deterministic case, first algorithm: a � z a � y x a a � v u a Filippo Bonchi & Damien Pous 4/26

  6. � � Checking language equivalence Deterministic case, first algorithm: a � z a � y x a a � v u a Filippo Bonchi & Damien Pous 4/26

  7. � � Checking language equivalence Deterministic case, first algorithm: a � z a � y x a a � v u a Filippo Bonchi & Damien Pous 4/26

  8. � � Checking language equivalence Deterministic case, first algorithm: a � z a � y x a a � v u a Filippo Bonchi & Damien Pous 4/26

  9. � � Checking language equivalence Deterministic case, first algorithm: a � z a � y x a a � v u a Filippo Bonchi & Damien Pous 4/26

  10. Checking language equivalence Deterministic case, naive algorithm, correctness: ◮ A relation R is a bisimulation if x R y entails ◮ o ( x ) = o ( y ); ◮ for all a , t a ( x ) R t a ( y ). Filippo Bonchi & Damien Pous 5/26

  11. Checking language equivalence Deterministic case, naive algorithm, correctness: ◮ A relation R is a bisimulation if x R y entails ◮ o ( x ) = o ( y ); ◮ for all a , t a ( x ) R t a ( y ). ◮ Theorem: L ( x ) = L ( y ) iff there exists a bisimulation R with x R y Filippo Bonchi & Damien Pous 5/26

  12. Checking language equivalence Deterministic case, naive algorithm, correctness: ◮ A relation R is a bisimulation if x R y entails ◮ o ( x ) = o ( y ); ◮ for all a , t a ( x ) R t a ( y ). ◮ Theorem: L ( x ) = L ( y ) iff there exists a bisimulation R with x R y The previous algorithm attempts to construct a bisimulation Filippo Bonchi & Damien Pous 5/26

  13. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · Filippo Bonchi & Damien Pous 6/26

  14. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 1 pairs Filippo Bonchi & Damien Pous 6/26

  15. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 2 pairs Filippo Bonchi & Damien Pous 6/26

  16. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 3 pairs Filippo Bonchi & Damien Pous 6/26

  17. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 4 pairs Filippo Bonchi & Damien Pous 6/26

  18. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 5 pairs Filippo Bonchi & Damien Pous 6/26

  19. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 6 pairs Filippo Bonchi & Damien Pous 6/26

  20. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 7 pairs Filippo Bonchi & Damien Pous 6/26

  21. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 8 pairs Filippo Bonchi & Damien Pous 6/26

  22. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 9 pairs Filippo Bonchi & Damien Pous 6/26

  23. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 10 pairs Filippo Bonchi & Damien Pous 6/26

  24. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 11 pairs Filippo Bonchi & Damien Pous 6/26

  25. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 12 pairs Filippo Bonchi & Damien Pous 6/26

  26. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 13 pairs Filippo Bonchi & Damien Pous 6/26

  27. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 14 pairs Filippo Bonchi & Damien Pous 6/26

  28. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 15 pairs Filippo Bonchi & Damien Pous 6/26

  29. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 16 pairs Filippo Bonchi & Damien Pous 6/26

  30. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 17 pairs Filippo Bonchi & Damien Pous 6/26

  31. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 18 pairs Filippo Bonchi & Damien Pous 6/26

  32. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 19 pairs Filippo Bonchi & Damien Pous 6/26

  33. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 20 pairs Filippo Bonchi & Damien Pous 6/26

  34. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 21 pairs Filippo Bonchi & Damien Pous 6/26

  35. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 21 pairs Filippo Bonchi & Damien Pous 6/26

  36. � � Checking language equivalence Deterministic case, naive algorithm: quadratic complexity � · � · � · � · · � · � · � · � · · 21 pairs Filippo Bonchi & Damien Pous 6/26

  37. � � Checking language equivalence One can stop much earlier � · � · � · � · · � · � · � · � · · 21 pairs Filippo Bonchi & Damien Pous 7/26

  38. � � Checking language equivalence One can stop much earlier � · � · � · � · · � · � · � · � · · 21 20 pairs Filippo Bonchi & Damien Pous 7/26

  39. � � Checking language equivalence One can stop much earlier � · � · � · � · · � · � · � · � · · 21 19 pairs Filippo Bonchi & Damien Pous 7/26

  40. � � Checking language equivalence One can stop much earlier � · � · � · � · · � · � · � · � · · 21 18 pairs Filippo Bonchi & Damien Pous 7/26

  41. � � Checking language equivalence One can stop much earlier � · � · � · � · · � · � · � · � · · 21 17 pairs Filippo Bonchi & Damien Pous 7/26

  42. � � Checking language equivalence One can stop much earlier � · � · � · � · · � · � · � · � · · 21 16 pairs Filippo Bonchi & Damien Pous 7/26

  43. � � Checking language equivalence One can stop much earlier � · � · � · � · · � · � · � · � · · 21 15 pairs Filippo Bonchi & Damien Pous 7/26

  44. � � Checking language equivalence One can stop much earlier � · � · � · � · · � · � · � · � · · 21 14 pairs Filippo Bonchi & Damien Pous 7/26

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