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Project-declaredLean 4.33.0-rc1 · mathlib@169c26b52a38

Dfa num state min

Language.dfa_num_state_min

Plain-language statement

All DFAs accepting l must have at least as many states as the number of equivalence classes of the Nerode congruence on l.

Exact Lean statement

theorem dfa_num_state_min {State : Type} {M : DA.FinAcc State α} [Finite State] :
    Nat.card State ≥ Nat.card (language M).NerodeQuotient

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
theorem dfa_num_state_min {State : Type} {M : DA.FinAcc State α} [Finite State] :    Nat.card State  Nat.card (language M).NerodeQuotient := by  let ws : Set (List α) := Set.range (Quotient.out : NerodeQuotient (language M)  List α)  have : Finite (language M).NerodeQuotient :=      IsRegular.iff_finite_nerodeQuotient.mp (IsRegular.iff_dfa.mpr State, inferInstance, M, rfl)  have : Finite ws := Set.finite_range _ |>.to_subtype  have hws : ws.Pairwise (fun x y  ¬((language M).NerodeCongruence).r x y) := by    rintro _ qx, rfl _ qy, rfl hne h    apply hne    simpa using Quotient.sound h  have h1 := dfa_num_state_ge hws rfl  rw [Nat.card_congr (Equiv.ofInjective _ Quotient.out_injective).symm] at h1  assumption
Project
Lean Computer Science Library
License
Apache-2.0
Commit
f36649cff2c9
Source
Cslib/Computability/Languages/MyhillNerode.lean:146-158

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Related declarations

Project-declaredLean 4.33.0-rc1

Unique minimal

Cslib.Automata.DA.FinAcc.unique_minimal

Plain-language statement

The minimal DFA M accepting the language l is unique up to unique isomorphism.

computer sciencecomputabilityprogram semantics

Source project: Lean Computer Science Library

Person-level attribution pending.

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Project-declaredLean 4.33.0-rc1

Buchi Family cover

Cslib.Automata.NA.Buchi.buchiFamily_cover

Project documentation

na.buchiFamily is a cover if na has only finitely many states. This theorem uses the Ramsey theorem for infinite graphs and does not depend on any details of na.BuchiCongruence other than that it is of finite index.

computer sciencecomputabilityprogram semantics

Source project: Lean Computer Science Library

Person-level attribution pending.

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