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Anisotropic isoperimetric double tilings of the plane

T0 review · 0 major / 4 minor · reviewed 2026-07-14 · grok-4.5

Pith's one-line read The cheapest way to tile the plane with two repeating cells under ℓ1 length is the Pythagorean arrangement of two axis-aligned squares that share a vertex.

desk verdict Clean L1 double-tiling classification: Pythagorean squares give the global profile, uniqueness holds for unequal areas, and the rectangular case is fully explicit. read the letter →

arxiv 2607.10636 v1 pith:GLOZBX4D submitted 2026-07-12 math.AP math.MG

classification math.APmath.MG MSC 49Q0552C2058E12
keywords tilingsanisotropicperimeterisoperimetricprofileℓ1-perimeterPythagoreantilingperiodicpartitionsWulffinequality
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper asks how to partition the plane into two families of identical cells so that the total length of interfaces, measured with the Manhattan (ℓ1) norm, is as small as possible for given cell areas. When the cells must repeat according to a fixed rectangular lattice, the optimal shapes switch from a square sitting inside a chipped rectangle (when one area is small) to a pair of adjacent rectangles (when the areas are comparable). Once every possible lattice is allowed, the global minimum is always achieved by two axis-aligned squares that share a single vertex—the classical Pythagorean tiling—and this arrangement is unique except when the two areas are equal. The same constructions remain locally optimal even after one cell area is sent to infinity, producing infinite-area “vortex” or “cross” partitions that cannot be improved inside any large box. The result supplies an explicit anisotropic counterpart to classical honeycomb and double-bubble theorems and shows that the ℓ1 geometry forces far more rigidity than the Euclidean perimeter.

What carries the argument

The (G,ℓ1)-isoperimetric profile IG,ℓ1(x) together with its global envelope Iℓ1(x); both are evaluated by combining the Wulff inequality for the ℓ1-perimeter with exhaustive case analysis on which generators are crossed by horizontal and vertical lines.

What would settle it

Exhibit any lattice of area 1 and any pair of generators of areas x and 1-x whose total ℓ1-perimeter is strictly smaller than 2√x + 2√(1-x), or show that a non-Pythagorean configuration saturates the bound for some x ≠ 1/2.

Watch

Extended reading notes

Core claim

For every area fraction x the global ℓ1-isoperimetric profile equals 2√x + 2√(1-x) and is realized uniquely (except at x = 1/2) by the Pythagorean double tiling of two axis-aligned squares sharing a vertex; for a fixed rectangular lattice the profile is piecewise explicit and the minimizers are completely classified as either a square-plus-chipped-rectangle or a pair of adjacent rectangles.

Load-bearing premise

The classification rests on the claim that every minimizer admits open, essentially bounded representatives whose topological boundaries coincide with their reduced boundaries, and that connectedness of one cell forces connectedness of the other.

Editorial extensions

If this is right

  • Any periodic double tiling that is not Pythagorean (or a rectangular pair when the lattice is fixed) can be improved by a pure lattice change or a shape change.
  • The infinite-area “vortex” and “cross” partitions obtained by sending one volume to infinity are locally ℓ1-minimizing, so they cannot be bettered inside any finite window.
  • When the two areas are equal the minimizers form infinite families of striped square packings, all sharing the same perimeter cost.
  • The squared excess (IG,ℓ1(x) - IG,ℓ1(0))² is concave, giving a quantitative concavity statement for rectangular lattices.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The same Wulff-plus-line-crossing method should classify triple or higher anisotropic tilings once the appropriate combinatorial cases are enumerated.
  • Because ℓ1 forces axis-alignment, the uniqueness statements are stronger than their Euclidean counterparts and may extend to other crystalline norms whose Wulff shapes are polygons.
  • Local minimality of the infinite partitions suggests they could serve as building blocks for free-boundary anisotropic cluster problems with mixed finite and infinite chambers.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

0 major / 4 minor

Summary. The paper studies periodic double tilings of the plane that minimize the anisotropic ℓ₁-perimeter. For a fixed rectangular lattice G of area 1, Theorem 1.1 gives an explicit formula for the (G,ℓ₁)-isoperimetric profile IG,ℓ₁(x) and classifies all minimizers: a square plus chipped rectangle when one cell is small, and two adjacent rectangles otherwise. Minimizing further over all planar lattices, Theorem 1.2 shows that Iℓ₁(x)=2√x+2√(1-x), attained uniquely (for x eq1/2) by the Pythagorean double tiling of two axis-aligned squares sharing a vertex; when x=1/2 the minimizers are alternating strips of equal squares. Theorem 1.4 then proves that certain limiting non-periodic partitions obtained by sending one volume to infinity are locally ℓ₁-isoperimetric. The arguments combine the classical Wulff inequality for the ℓ₁-norm with elementary projection estimates and a finite case analysis on how horizontal and vertical lines meet the generators.

Significance. The work supplies a complete, explicit solution of the anisotropic double-tiling problem for the Manhattan perimeter, both for rectangular lattices and after free minimization over all lattices. The profile formula of Theorem 1.2 is parameter-free and is realized by a classical geometric construction (the Pythagorean tiling), while uniqueness follows from the rigidity of the Wulff shape. The classification for rectangular lattices and the local-minimality statements for infinite-volume partitions extend the authors’ earlier isotropic results and fit naturally into the ongoing program on anisotropic clusters and periodic partitions. The proofs are elementary once the Wulff inequality and the projection lemmas are in place, and the geometric models are fully explicit.

minor comments (4)
  1. In the proof of Theorem 3.5 the density constants are obtained by covering a fundamental domain with finitely many balls and taking the worst-case constants from Theorem 3.4; a one-sentence remark that the resulting c,ρ₀ depend only on G and φ (and not on the particular tiling) would make the uniformity claim fully transparent.
  2. Lemma 3.7 asserts connectedness of E₂ whenever R^{2}\(Ē₁+G) is connected. The argument is short and correct, but a brief parenthetical note that the same conclusion holds after replacing E₁ by any finite union of its G-translates would clarify why the construction (3.3) preserves the property.
  3. Figure 4 and the accompanying text in the introduction describe a continuum of energetically equivalent placements of the small square; it would help the reader if the precise range of admissible (h,l) were stated once in the body of Theorem 1.1 rather than only in the caption.
  4. A few typographical inconsistencies appear (e.g., “prescrived” on p. 15, “horizonal” on p. 15, and the occasional missing space before parentheses). A light copy-edit pass would remove them.

Circularity Check

0 steps flagged · score 1.0 of 10

No significant circularity: profile lower bound is classical Wulff, upper bound explicit competitor; self-citations only for existence/context.

full rationale

The central claim of Theorem 1.2 follows by the classical Wulff inequality (2.2) giving I_ℓ1(x) ≥ 2√x + 2√(1-x), matched by the explicit Pythagorean competitor of two axis-aligned squares; uniqueness is a short geometric rigidity argument forcing lattice vectors of the form (a,h),(w,a) with w=h=√x (or strips when x=1/2). Theorem 1.1 is obtained by case analysis on line-touching properties plus elementary projection estimates (Lemmas 4.1–4.5) and the same Wulff bound, with equality cases classified by connectedness and rectangle characterization (Lemma 4.2). Existence (Theorem 3.1) and density/regularity (Theorems 3.4–3.5, Corollary 3.6) cite the authors’ prior isotropic work [NN24] and standard GMT references, but these supply only the existence of minimizers and open representatives; the numerical value of the profile and the geometric models are derived independently and do not reduce to those citations. No fitted parameters, self-definitional identities, or load-bearing uniqueness theorems imported from the authors appear. The derivation is therefore self-contained against external benchmarks.

Assumptions & free parameters 0 free parameters · 3 assumptions · 0 invented entities

The paper works entirely inside classical geometric measure theory. The only external inputs are the Wulff inequality for the L1 norm (standard) and the existence/regularity theory for anisotropic isoperimetric tilings developed in the authors’ earlier papers; no free parameters or new physical entities are introduced.

assumptions (3)
  • standard math Wulff inequality for the L1 norm: Per_ℓ₁(E)≥4√|E| with equality precisely for axis-aligned squares (Theorem 2.1 / (2.2)).
    Classical result used as the lower bound for every generator; equality case supplies uniqueness of squares.
  • domain assumption Existence of a φ-isoperimetric N-tiling with essentially bounded generators when d=2 (Theorem 3.1, citing NN24).
    Guarantees that minimizers exist and can be taken open and bounded so that the subsequent topological arguments apply.
  • domain assumption Density estimates for volume-constrained anisotropic partitions (Theorem 3.4).
    Used to obtain open representatives with H^{1}( abla E\nabla*E)=0; proof is omitted as standard.

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Pith. "Pith review of Anisotropic isoperimetric double tilings of the plane." pith.science (2026). https://pith.science/paper/GLOZBX4D

@misc{pith2026260710636,
  author       = {Pith},
  title        = {Pith review of: Anisotropic isoperimetric double tilings of the plane},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/GLOZBX4D}},
  note         = {Machine review of arXiv:2607.10636}
}
abstract

We study periodic partitions of the plane into two distinct cells minimizing the anisotropic $\ell_1$-perimeter. For a rectangular lattice $G$, we compute explicitly the $(G,\ell_1)$-isoperimetric profile and classify all minimizers. When one cell has small area, the optimal tiling is generated by a square and a chipped rectangle, while in the remaining regime the tiling is generated by two adjacent rectangles. Further minimizing over all possible planar lattices, we show that the $\ell_1$-isoperimetric profile is attained by the Pythagorean double tiling of two axis-aligned squares sharing a vertex. This configuration is unique unless the two cells are assigned the same area. Finally, we prove that the limiting (non periodic) partitions obtained by sending one volume to infinity are locally $\ell_1$-isoperimetric.

Figures

Figures reproduced from arXiv: 2607.10636 by the authors.

Figure 1
Figure 1. Isoperimetric profile IG,ℓ1 (x) [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. The ℓ1-isoperimetric double tiling generated by a square and a chipped rectangle [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. The ℓ1-isoperimetric double tiling generated by two adjacent rectangles. Instead, when x ∈ (0, 1), the minimizers are also completely classified, and the minimizing models are depicted in [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figures from the paper (5 more)
Figure 4
Figure 4. Figure 4: Given x ≤ b 2 4 , any choice of E1 (red) and E2 (white) with h, l ∈ [0, √ x] generates a double tiling with perimeter equal to IG,ℓ1 (x) [PITH_FULL_IMAGE:figures/full_fig_p005_4.png]
Figure 5
Figure 5. Figure 5: Example of generators with same total ℓ1-perimeter. profile function defined by [0, 1] ∋ x 7→ Iℓ1 (x) := inf{IG,ℓ1 (x): G lattice with Area(G) = 1}. For the standard perimeter (i.e. for the choice of anisotropic norm given by φ(x) = ∥x∥ℓ2 ), the above was considered by…
Figure 6
Figure 6. Figure 6: The Pythagorean double tiling [PITH_FULL_IMAGE:figures/full_fig_p006_6.png]
Figure 7
Figure 7. Figure 7: Possible partitions obtained by sending |E2| ↑ ∞ while keeping |E1| = 1 on the isoperimetric double tilings: the first three partitions are obtained from Case i) in Theorem 1.1, the last one (the vortex ) is obtained from Theorem 1.2. induced by any of the ℓ1-isoperime…
Figure 8
Figure 8. Figure 8: A possible ℓ1-isoperimetric double tiling composed of two cells of equal area and with the same perimeter of the Pythagorean double tiling. 2. Preliminaries In this section, we recall some useful facts around the classical and anisotropic perimeters. 2.1. Sets of finit…

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