Route a invertible
v301_route_a_invertible.py · frontier
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SEAM.EQUIV.A.INV.01 — discharge Route A's single open hypothesis (v297 LIT-A: 'the raw quasi-free seam bulk is invertible/SRE') via the free-fermion classification. Since v300 collapsed Route B into Route A, this is the LAST unconditional gap of SEAM.EQUIV.01. [E] carrier = 16 Majoranas, c=8: g_car+N_fam=5+3=8=16/2 (v148). [E] SO(16)₁ ⊃ (E8)₁: dim so(16)=120 currents + 128 spinor = 248 = dim E8 (v154). [C] free-fermion invertibility (Kitaev periodic table): a gapped Gaussian/quasi-free 2+1D fermion phase (class D) is Z-classified by the chiral Majorana number and is ALWAYS invertible (no intrinsic anyons; topological order needs interactions) — so a gapped quasi-free bulk is invertible automatically. [E] invariant |det K|=#anyons: E8 Cartan det=1 (invertible) vs the gauged contrast D8=SO(16) det=4 (anyons), which free fermions cannot produce. [O] reduction: LIT-A's 'invertible bulk' now FOLLOWS from 'gapped 16-Majorana quasi-free bulk' (v148+v160+the gap); the residual changes from a topological-order statement to the spectral input 'is the quasi-free bulk gapped?'. [O] verdict: with v300 the WHOLE open content of SEAM.EQUIV.01 reduces to the single spectral statement 'the quasi-free seam bulk is gapped'.
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