Maximum Weight Independent Set in Hereditary Classes of Ordered Graphs
Pith reviewed 2026-05-08 01:31 UTC · model grok-4.3
The pith
For every ordered graph H, MWIS on H-free ordered graphs is polynomial, quasipolynomial, subexponential, or NP-hard, with subexponential time only for one specific family of H.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The authors prove that for every ordered graph H, the Maximum Weight Independent Set problem on ordered graphs excluding H as an induced subgraph is solvable in polynomial time, quasipolynomial time, subexponential time, or is NP-hard. The subexponential case arises only for one well-structured family of forbidden graphs H, namely those obtained from two nested edges by adding isolated vertices in a specific way. As a direct consequence, apart from this family the problem is either solvable in quasipolynomial time or NP-hard, yielding an almost complete complexity dichotomy for MWIS in hereditary classes of ordered graphs defined by a single forbidden induced subgraph.
What carries the argument
The forbidden ordered graph H, whose structural form (specifically membership in the two-nested-edges family with prescribed isolated vertices) determines whether MWIS is polynomial, quasipolynomial, subexponential, or NP-hard.
Load-bearing premise
The input consists of ordered graphs whose linear vertex ordering is fixed and given as part of the instance, and the hereditary class is defined by excluding exactly one ordered graph H as an induced subgraph.
What would settle it
An ordered graph H outside the two-nested-edges-plus-isolates family for which MWIS on H-free ordered graphs admits neither a quasipolynomial-time algorithm nor an NP-hardness proof, or conversely an H inside that family for which the problem requires super-quasipolynomial yet subexponential time.
Figures
read the original abstract
The complexity of classical computational problems in graph classes defined by forbidding induced subgraphs is one of the central topics of algorithmic graph theory. Recently, there has been a growing interest in the complexity of such problems in ordered graphs, i.e., graphs with a fixed linear ordering of vertices. Such an approach allows us to investigate the boundary of tractability more closely. However, most results so far concern coloring problems. In this paper, we focus on the complexity of the Maximum Weight Independent Set (MWIS) problem in classes of ordered graphs. For every ordered graph $H$, we classify the complexity of MWIS in ordered graphs that exclude $H$ as an induced subgraph into one of the following cases: (1) solvable in polynomial time, (2) solvable in quasipolynomial time, (3) solvable in subexponential time, (4) NP-hard. Notably, case (3) contains only one well-structured family of $H$ obtained from two nested edges by adding isolated vertices in a specific way. Thus, our results yield an almost complete complexity dichotomy for MWIS in classes of ordered graphs defined by a single forbidden induced subgraph into cases solvable in quasipolynomial time and those that are NP-hard.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript classifies the complexity of Maximum Weight Independent Set (MWIS) on ordered graphs excluding a single ordered graph H as an induced subgraph. For every such H the problem falls into one of four regimes: polynomial-time solvable, quasipolynomial-time solvable, subexponential-time solvable (only for the specific family obtained from two nested edges by adding isolated vertices in a prescribed manner), or NP-hard. The result is presented as yielding an almost-complete dichotomy between the quasipolynomial and NP-hard cases.
Significance. If the classification is correct, the paper supplies a fine-grained complexity map for MWIS in hereditary classes of ordered graphs defined by a single forbidden induced ordered subgraph. This extends the existing literature on ordered graphs (previously focused mainly on coloring) and isolates the subexponential case to a single, explicitly described family, which is a structurally clean outcome. The work thereby sharpens the boundary between tractable and intractable regimes for this problem.
minor comments (3)
- [Abstract] Abstract, final sentence: the claim of a 'complete classification into four cases' is immediately followed by 'almost complete complexity dichotomy'; this tension should be resolved by a precise statement of what, if anything, remains open after the four-way partition.
- [Introduction] The formal definition of the 'two nested edges plus isolates' family (the sole subexponential case) appears only in the abstract; an early figure or a self-contained definition in Section 1 would improve readability for readers who wish to verify membership of a given H.
- [Preliminaries] Notation for ordered graphs and induced subgraphs is introduced gradually; a single consolidated notation paragraph or table at the beginning of the preliminaries would reduce cross-referencing.
Simulated Author's Rebuttal
We thank the referee for their positive assessment of the manuscript, including the summary of our classification results and the significance statement. The recommendation for minor revision is noted. No major comments were provided in the report.
Circularity Check
No significant circularity identified
full rationale
The paper presents a structural complexity classification of MWIS on ordered graphs excluding a single induced ordered subgraph H. The stated dichotomy (P, quasipolynomial, subexponential only for one explicit family of nested-edge-plus-isolates H, or NP-hard) is derived from case analysis on the structure of H rather than from any fitted parameter, self-defined quantity, or load-bearing self-citation that reduces the result to its own inputs. No equations, ansatzes, or predictions appear in the abstract or described claim; the classification is presented as a direct enumeration of cases. This matches the default expectation for a non-circular theoretical dichotomy in algorithmic graph theory.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Standard complexity-theoretic assumptions (P ≠ NP, subexponential time classes are distinct from polynomial and NP-hard regimes)
- domain assumption Ordered graphs are graphs with a fixed linear vertex ordering; induced subgraphs respect both edges and the ordering.
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