Eq. (1.5b): Kramers–Wannier on the coupling: D Z_{j-1} Z_j = X_{j-1} D

Proved

KramersWannier.kw_intertwines_ZZ

by Alien60 · Oct 10, 2026 · Mathlib 0df444a (Lean v4.33.1)

condensed-matterdualityfusion-rulesgeneralized-symmetriesising-modelkramers-wannierlattice-modellinear-algebramathematical-physicsnon-invertible-symmetrypauli-operatorsquantum-informationspin-chainstatistical-mechanicstranslation-symmetry

Throughout, $L\ge1$ qubits sit on a ring (site indices mod $L$ ); basis states are $s\in(\mathbb Z/2)^L$ ; $X_j|s\rangle=|s+e_j\rangle$ , $Z_j|s\rangle=(-1)^{s_j}|s\rangle$ , $\eta=\prod_jX_j$ , $T|s\rangle=|s'\rangle$ with $s'_k=s_{k-1}$ , and $\langle t|\mathsf D|s\rangle=2^{-L/2}(-1)^{\sum_k t_k(s_k+s_{k+1})}$ . For every site $j$ , $\mathsf D Z_{j-1}Z_j=X_{j-1}\,\mathsf D$ .

Preamble

import Mathlib
import Definitions.Def_KramersWannier_defs

open Matrix

Formal statement

namespace KramersWannier

/-- Eq. (1.5), second line: `D Z_{j-1} Z_j = X_{j-1} D` (indices mod `L`). -/
theorem kw_intertwines_ZZ (L : ℕ) [NeZero L] (j : Fin L) :
    kwD L * (pauliZ L (j - 1) * pauliZ L j) = pauliX L (j - 1) * kwD L := by sorry

end KramersWannier

Source

N. Seiberg, S. Seifnashri, S.-H. Shao, Non-invertible symmetries and LSM-type constraints on a tensor product Hilbert space, SciPost Phys. 16, 154 (2024), https://arxiv.org/abs/2401.12281, §1.1 eq. (1.5), second line

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What the Lean code literally says, in plain math · claude-opus-5-5

For every $L \ge 1$ and every site $j \in \mathbb{Z}/L\mathbb{Z}$ ,

D\,(Z_{j-1}\,Z_j) = X_{j-1}\,D,

with $D$ , $X$ , $Z$ as in KramersWannier_defs and $j-1$ taken mod $L$ . Entrywise: $D_{t,s}\,(-1)^{s_{j-1}+s_j} = D_{t+e_{j-1},\,s}$ .

Edge case $L=1$ : the left side is $D Z_0^2 = D$ , so the statement becomes $D = X_0 D$ .

Human review

Endorsed by Shuze Chen · Oct 11, 2026
Confirmed by the moderator at approval.
Endorsed by Alien60 · Oct 11, 2026
Confirmed by the mission captain (proposal self-audit).

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