Recognition: unknown
Exact Flatness Constant for One-Point Convex Bodies and the Discrete Isominwidth Problem: The Planar Case
Pith reviewed 2026-05-07 10:24 UTC · model grok-4.3
The pith
Any planar convex body with at most one interior lattice point has lattice width at most 3.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The authors show that Flt(2,1) = 3. Every convex body in R^2 with at most one interior lattice point therefore has lattice width at most 3, and this value is tight. The proof combines supporting-line arguments with enumeration of possible interior-point configurations to obtain both the upper bound and matching examples.
What carries the argument
The flatness constant Flt(d,k), the supremum of lattice widths taken over all convex bodies in R^d that contain at most k interior lattice points.
If this is right
- The exact value yields an isominwidth inequality that bounds the lattice-point enumerator of any planar convex body from below by a function of its isominwidth.
- It confirms the planar case of the discrete isominwidth problem.
- It supplies the missing exact constant needed to relate the classical flatness problem to Makai's conjectural dual form of Minkowski's theorem.
Where Pith is reading between the lines
- The width bound could be used to restrict the feasible region in 2D integer linear programs before enumeration.
- The same geometric technique might determine Flt(3,1) or the value for other small k in the plane.
- It constrains the possible areas and shapes of convex bodies that are nearly lattice-point free.
Load-bearing premise
Convex bodies are closed sets in the plane and the lattice is the standard integer lattice Z^2, with width measured as the minimum distance between parallel supporting lines.
What would settle it
A single closed convex set in the plane that contains at most one interior integer point yet has lattice width 4 or greater would disprove the equality.
Figures
read the original abstract
A variant of the flatness problem from integer programming is studied, in which one considers convex bodies in $\mathbb{R}^d$ with at most $k$ interior lattice points. The maximum lattice width of such a body is denoted by Flt(d,k) and it is related to the classical flatness constant as well as a conjectural dual version of Minkowski's convex body theorem due to Makai. Moreover, it is shown that Flt(2, 1) = 3, i.e., any planar convex body with at most one interior point has lattice width at most three. This leads to an isominwidth inequality for the lattice point enumerator of planar convex bodies.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript defines Flt(d,k) as the maximum lattice width attained by any convex body in R^d with at most k interior lattice points. It proves that Flt(2,1)=3, i.e., every planar convex body with at most one interior lattice point has lattice width at most 3. The upper bound is established by exhaustive case analysis of the possible positions of the (at most one) interior point relative to a minimal-width direction; sharpness is shown by an explicit example attaining width exactly 3. The result is applied to obtain an isominwidth inequality relating the lattice-point enumerator of planar convex bodies to their minimal width.
Significance. If the result holds, it supplies the exact flatness constant for the one-interior-point case in the plane, resolving a concrete instance of the flatness problem and its discrete isominwidth variant. The proof relies on elementary convex geometry and exhaustive enumeration of configurations in Z^2, together with an explicit attaining example; these elements constitute a self-contained and verifiable argument. The derived inequality provides a new quantitative relation between width and lattice-point count that may be useful in integer programming and discrete geometry.
minor comments (3)
- [§2] §2: The definition of lattice width via supporting lines is standard but should be recalled with the explicit formula w_L(K) = min_{u in Z^2, ||u||=1} (max <x,u> - min <x,u>) to make the subsequent case analysis self-contained for readers outside the immediate subfield.
- [Theorem 1.1 and §4] Theorem 1.1 and the example in §4: The attaining body (a specific polygon with one interior point) is described geometrically; adding the explicit vertex coordinates and verification that it contains exactly one interior lattice point would allow immediate independent checking of sharpness.
- [Figure 1] Figure 1 (case-analysis diagram): The diagram illustrating the relative positions of the interior point is useful, but the arrows indicating the minimal-width direction and the lattice points should be labeled more clearly to match the textual cases.
Simulated Author's Rebuttal
We thank the referee for their careful reading, positive evaluation, and recommendation of minor revision. The report accurately summarizes the main result establishing Flt(2,1)=3 and its applications. No specific major comments were raised in the report.
Circularity Check
No significant circularity identified
full rationale
The manuscript proves the central claim Flt(2,1)=3 via an exhaustive case analysis of the possible positions of the (at most one) interior lattice point relative to a minimal-width direction, together with an explicit convex body attaining width exactly 3. This argument rests only on the standard definitions of lattice width, supporting hyperplanes, and convex bodies in the plane with respect to Z^2; no quantity is fitted to data and then renamed as a prediction, no self-citation supplies a load-bearing uniqueness theorem or ansatz, and the equality is not obtained by construction from the inputs. Prior conjectures are cited only for context and do not enter the derivation chain.
Axiom & Free-Parameter Ledger
axioms (3)
- standard math Convex bodies are closed subsets of R^d that contain the line segment between any two of their points.
- standard math The lattice is the standard integer lattice Z^d with the usual Euclidean norm for width calculations.
- domain assumption Lattice width is defined via the minimum over integer directions of the difference between supporting hyperplanes.
Reference graph
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