
all a ∈ A, b ∈ B, then dim A+dim B ≤ n
X
+n
Z
−r. Proof. The map a 7→ a
T
M sends A into the in-
tersection of the row space of M (dimension r) with the annihilator of B (dimension n
Z
−dim B), and
its kernel lies in the left kernel of M (dimension n
X
−r); hence dim A ≤ (n
X
−r)+min(r, n
Z
−dim B),
and both branches of the minimum give dim A+dim B ≤ n
X
+n
Z
−r. □ Retaining the full Z-space
and restricting X to the kernel therefore attains the joint optimum; sacrificing Z-checks can never
purchase more total generators. On the reference patch we measure r = 66, so the completion keeps
542 of 608 generators; the explicit construction (all 306 Z-checks together with the 236-dimensional
X-subgroup annihilating M ) saturates this bound, and direct verification confirms every pair even.
Under the completed stabilizer set the polycrystalline vacuum is again exactly zero code energy.
The boundary’s cost is paid in a different currency: a check deficit of 66 on the reference patch,
approximately one surrendered stabilizer per bond
2
of seam (1.006/bond
2
measured; 0.83 ± 0.12
across the orientation ensemble below). Adversarial grain boundaries, in this framework, cost
check structure, not energy (the kinematically preferred population costs neither; see below)—and
where checks are surrendered, that structure is a natural home for the seam-localized freedom in
which the framework’s inter-grain frame-translation processes operate; whether it resolves into local
logical or gauge modes is characterized, to the extent the patch permits, in the parameter count
below.
Completed code parameters and generator locality. On the reference patch the completed
bicrystal code has n = 3704 edge qubits, rank(H
Z
) = 306, rank(H
compl
X
) = 236, hence k = 3162; a
single-crystal patch on the identical window and interior filter has n = 3620, ranks 365 + 364 = 729,
k = 2891, and zero odd pairs. The seam therefore costs 187 independent constraints relative to
the reference (≈ 2.9/bond
2
): 121 candidate checks destroyed outright by misorientation, plus the
66 surrendered to frustration. The completion is nearly local: 231 of its 236 X-generators are
single original weight-12 octahedral checks, and the remaining five are combinations of weight 56–
120 confined to a half-bond-thick layer hugging the seam (z ∈ [−1.5, −1.0]) but laterally extended
across the full patch—seam-parallel sheet operators.
Patch-size scaling of the sheet generators. Repeating the construction at the same orienta-
tion on windows of seam area 65.6, 144, and 253 bond
2
gives sheet-generator counts of 5, 7, and 8,
with maximum weights 120, 224, and 284: in the constructed (echelon nullspace) basis, the sheets
span the full lateral window at every size and their weights grow with the window. The frustration
rank density stays at order one per bond
2
(1.006, 1.007, 0.886) across the sweep. The completion
is therefore not demonstrated to be local in the thermodynamic limit: the decisive open question
is whether the same commuting subgroup admits a different, bounded-weight generating basis, or
whether every compatible completion necessarily contains seam-spanning sheet operators. A full
construction of the added logical operators, and a proof of their seam localization, likewise remains
open. (On open-window patches, k is dominated by window-boundary freedom, and the bicrystal
and reference qubit sets differ, so raw k-differences must not be read as seam logical freedom; the
constraint accounting above is the meaningful comparison, and a direct boundary logical count
requires matched qubit spaces or a relative-homology construction.)
Pilot orientation ensemble. Across six Haar-random relative orientations (including the refer-
ence), the seam statistics are: odd pairs 195 ± 27 (range 163–239), frustration rank r = 54.5 ± 8.1,
check deficit 0.83±0.12 per bond
2
, and matching bound 58.5±8.1, giving a frustration-energy lower
bound of 0.26 ± 0.04 J per bond
2
. The reference patch sits at the high end of this distribution; all
qualitative conclusions—frustration under naive truncation, existence and predominant finite-patch
5