A6 chambers are W33 spreads.

An exact, objectwise U4(2)-equivariant bridge—plus an executable certificate for the exceptional outer automorphism of S6.

36 ↔ 36

Every A6 chamber determines one unique W33 spread.

720 → 360

The spread stabilizer is S6; its derived subgroup is the attached A6.

25 checks

The complete construction is frozen under a semantic SHA-256 certificate.

The canonical map

For a chamber H ≅ A6, the normalizer has order 720, fixes exactly one spread ΣH, and equals its spread stabilizer:

NG(H) = StabG(ΣH)

Transport under the four explicit U4(2) generators is path-independent. Therefore H ↦ Σ_H is an actual equivariant bijection, not a 36=36 analogy.

Intersection dictionary

A6 chamber intersectionSpread intersectionPairsRelation
|H ∩ K| = 181 shared line360SRG(36,20,10,12)
|H ∩ K| = 124 shared lines270SRG(36,15,6,6)

The two relations are complementary. The graph identity is carried by the explicit object map; parameters alone are not used as identification evidence.

The exceptional S6 double-six

6 + 6

The twelve A5 subgroups in one chamber split into the two global A5 classes.

A4 / D10

Same-side pairs meet in A4; every cross-pair meets in D10, yielding K6,6.

The S6 stabilizer acts faithfully on both six-sets. The two actions exchange cycle types exactly as the exceptional outer automorphism requires:

(2,1,1,1,1) ↔ (2,2,2), (3,1,1,1) ↔ (3,3), and (6) ↔ (3,2,1).

The directed multiplicities are 15, 40, and 120 in each direction.

Monster-facing meaning

A concrete 5B-containing U4(2) embedding in the Monster would automatically transport the full 36-spread carrier, all 36 A6 chambers, both rank-three orbitals, and all local double-six charts. This sharply specifies what a future Monster-word certificate must preserve.

Evidence boundary. This packet does not serialize Monster words, choose a unique class fusion, prove an 81-dimensional restriction multiplicity, identify the distinct 36 magic-ray graph, or construct a Griess, VOA, Leech, or photonic multiplication law.

Executable evidence

analysis/w33_pass3663_3669_monster_chamber_spread_bridge.py

data/PART_3663_3669_MONSTER_CHAMBER_SPREAD_BRIDGE_results.json

tests/test_w33_pass3663_3669_monster_chamber_spread_bridge.py

Semantic SHA-256: ea0d3d989c05d51dc1e60de05cb9fe9f3308d8c36f1e40749b915f7bc0aaefca