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arxiv: 2211.08787 · v6 · submitted 2022-11-16 · 💻 cs.FL

On Minimization and Learning of Deterministic ω-Automata in the Presence of Don't Care Words

Pith reviewed 2026-05-24 11:27 UTC · model grok-4.3

classification 💻 cs.FL
keywords deterministic omega-automataparity automatadon't care wordsminimizationright-congruenceweak deterministic Büchi automataactive learningNP-hardness
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The pith

The number of priorities in deterministic parity automata can be minimized efficiently under arbitrary don't care words.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that the number of priorities required by a deterministic parity automaton can be reduced to the minimum in polynomial time when an arbitrary set of words is designated as don't cares. This follows from a general minimization procedure that also produces an efficient algorithm for the case of deterministic parity automata with informative right-congruence in the absence of don't cares. For don't care sets whose right-congruence is trivial, weak deterministic Büchi automata possess a unique minimal representative that is characterized by a congruence relation and can be constructed efficiently. The same trivial right-congruence condition does not preserve uniqueness for automata with informative right-congruence, and minimization in that setting is NP-hard. The authors further extend an existing active learning procedure for weak deterministic Büchi automata to accept an additional don't care set with trivial right-congruence.

Core claim

The number of priorities in a deterministic parity automaton can be minimized in polynomial time under an arbitrary don't care set. This is obtained from a general minimization procedure applicable to deterministic parity automata that possess an informative right-congruence. For the subclass of weak deterministic Büchi automata and don't care languages whose right-congruence is trivial, the minimal automaton is unique and can be computed efficiently; it is characterized by the congruence that merges states indistinguishable under the don't care condition. In contrast, when the automata have informative right-congruence, even with trivial don't care congruence, there is no unique minimal wDB

What carries the argument

The general minimization procedure for deterministic parity automata under don't care conditions that reduces the priority count while preserving acceptance behavior.

If this is right

  • An efficient algorithm exists to minimize priorities in any deterministic parity automaton given any don't care set.
  • The same general result yields an efficient minimization for deterministic parity automata with informative right-congruence without don't cares.
  • Weak deterministic Büchi automata admit a unique minimal form under don't care sets with trivial right-congruence, characterized by a specific congruence.
  • Minimization of deterministic automata with informative right-congruence under trivial right-congruence don't cares is NP-hard.
  • The active learning algorithm for weak deterministic Büchi automata can be extended to handle don't care words with trivial right-congruence.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The separation between trivial and informative right-congruences may guide the design of don't care handling in other classes of omega-automata.
  • One could investigate whether similar priority minimization techniques apply to nondeterministic parity automata or other acceptance conditions.
  • Practical implementations of the learning extension might improve specification mining when some behaviors are unspecified.

Load-bearing premise

The results on uniqueness and efficient computation for weak deterministic Büchi automata hold only when the don't care words induce the trivial right-congruence.

What would settle it

A deterministic parity automaton together with a don't care set for which no polynomial-time procedure produces an equivalent automaton with the fewest priorities.

Figures

Figures reproduced from arXiv: 2211.08787 by Christof L\"oding, Max Philip Stachon.

Figure 1
Figure 1. Figure 1: Illustration of DON’T CARE PRIORITY OPTIMIZATION. An optimal parity condition consistent with (F ′ 0 , F ′ 1 ) can redefine the priority of q0 to 2 and thus use one priority less. there is no deterministic ω-automaton B of the same type with L(A) ≡D L(B) with less states than A. 3. Priority optimization In this section we consider the problem of optimizing a parity condition under a given don’t care set, r… view at source ↗
Figure 2
Figure 2. Figure 2: The DBA A has 3 different corresponding D-minimal DBA for the set of don’t care words D := Σ ∗ b ω. Proof: Consider the DBA A in [PITH_FULL_IMAGE:figures/full_fig_p011_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The D′ -minimal DPA Acol and the DPA AG for G = ({v1, v2, v3}, {(v1, v2),(v1, v3)}) recognize D′ -equivalent ω-languages. The don’t care set then includes all words α in which labels of the form xv occur infinitely often, or from some point on successive vertices vv′ in α are not connected by an edge. With this don’t care set, a D-minimal DPA Acol can use one state for each color class in a k-coloring inst… view at source ↗
Figure 4
Figure 4. Figure 4: The situation described in Lemma 5.3 with [PITH_FULL_IMAGE:figures/full_fig_p015_4.png] view at source ↗
read the original abstract

We study minimization problems for deterministic $\omega$-automata in the presence of don't care words. We prove that the number of priorities in deterministic parity automata can be efficiently minimized under an arbitrary set of don't care words. We derive that from a more general result from which one also obtains an efficient minimization algorithm for deterministic parity automata with informative right-congruence (without don't care words). We then analyze languages of don't care words with a trivial right-congruence. For such sets of don't care words it is known that weak deterministic B\"uchi automata (WDBA) have a unique minimal automaton that can be efficiently computed from a given WDBA (Eisinger, Klaedtke 2006). We give a congruence-based characterization of the corresponding minimal WDBA, and show that the don't care minimization results for WDBA do not extend to deterministic $\omega$-automata with informative right-congruence: for this class there is no unique minimal automaton for a given don't care set with trivial right congruence, and the minimization problem is NP-hard. Finally, we extend an active learning algorithm for WDBA (Maler, Pnueli 1995) to the setting with an additional set of don't care words with trivial right-congruence.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. The paper claims to prove that the number of priorities in deterministic parity automata can be efficiently minimized under an arbitrary set of don't care words. This follows from a more general result that also yields an efficient minimization algorithm for deterministic parity automata with informative right-congruence (without don't cares). For don't care words with trivial right-congruence, it gives a congruence-based characterization of the minimal weak deterministic Büchi automaton (extending Eisinger-Klaedtke 2006) and shows that uniqueness and efficient computability fail for the informative right-congruence case, where minimization is NP-hard. It also extends the Maler-Pnueli active learning algorithm for WDBA to the don't-care setting with trivial right-congruence.

Significance. If the results hold, they advance automata theory by supplying efficient priority-minimization procedures for parity automata under don't cares—an important class for verification and synthesis—and by cleanly delineating the boundary between the tractable (trivial right-congruence) and intractable (informative right-congruence) cases for WDBA. The derivation of multiple positive results from a single general theorem is a strength, as is the explicit extension of the 1995 learning algorithm. These contributions are directly usable in tools that manipulate ω-automata.

minor comments (2)
  1. [Abstract] Abstract: the statement that minimization is 'efficient' would be strengthened by naming the complexity class (e.g., polynomial time) rather than leaving it implicit.
  2. The manuscript states proofs and complexity results clearly in the abstract, but the absence of explicit algorithm pseudocode or a high-level complexity analysis in the provided summary text makes independent verification of the claimed polynomial-time bounds more difficult.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive evaluation and the recommendation of minor revision. The provided summary accurately captures the paper's contributions on priority minimization for deterministic parity automata under don't care words, the general result, the congruence characterization for trivial right-congruence WDBA, the NP-hardness result for informative right-congruence, and the extension of the Maler-Pnueli learning algorithm.

Circularity Check

0 steps flagged

No significant circularity; derivation relies on external citations and standard automata properties

full rationale

The paper's central positive claims (efficient minimization of priorities in DPA under don't cares, and for informative right-congruence) are stated as proven results derived from a general theorem, without reducing to self-definitions or fitted inputs. The WDBA uniqueness result is explicitly attributed to the external Eisinger-Klaedtke 2006 paper (different authors), and the learning extension builds on Maler-Pnueli 1995. Negative results (non-uniqueness and NP-hardness for informative right-congruence) are established via explicit counterexamples and hardness arguments. No load-bearing self-citation chains, ansatzes smuggled via citation, or renamings of known results appear in the provided abstract and claims. The derivation chain is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The paper relies on standard automata-theoretic concepts such as right-congruences and parity acceptance conditions. No free parameters are fitted to data. No new entities are postulated.

axioms (2)
  • standard math Right-congruence relations on words induce equivalence classes that determine automaton states and minimality
    Invoked throughout for characterizations of minimal automata and for distinguishing trivial vs. informative cases.
  • standard math Deterministic omega-automata acceptance is defined via parity or Büchi conditions on infinite runs
    Background assumption used to define the automata classes under study.

pith-pipeline@v0.9.0 · 5765 in / 1528 out tokens · 38269 ms · 2026-05-24T11:27:15.972889+00:00 · methodology

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