Proposition 7.2(1): W(P) ≅ ℤ^{n−1} ⊕ G_ab #
weights-and-parameters.tex (prop:integral-ray-weights(1)): "There is an identification
W(P) = (I_𝓛)_G […] the class θ_g of e_{gx} − e_x is independent of the object x, and
g ↦ θ_g identifies G_ab with a direct summand of W(P) with complement ℤ^{n−1}:
W(P) ≅ ℤ^{n−1} ⊕ G_ab."
With the deck group G of the base component (Hs, the stabilizer of the component 𝓛₀ of the
base object in the deck group of the coned complex; see RayWeights.lean):
W(P) = (I_𝓛₀)_G:[Σ v_o e_o] ↦ Σ v_o ζ(o)is an isomorphism (coinvEquiv), with inverseβWbuilt fromΨ;- the comparison
ΨofRayWeights.leanis an isomorphism onto the vectors with coordinate sum zero timesG_ab(ΨW_ΦW,WPequiv), henceW(P) ≃ ℤ^{n−1} × G_ab(WPequivFree); θ_g = ζ(gx) − ζ(x)does not depend onxin𝓛₀and is theG_absummand underWPequivFree(theta_summand).W(P)is free of finite rank (WP_free,WP_finite).
The class in H_ab of an object of the base component: κ(x, b) = b · a_x⁻¹.
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Ψ on differences of object values in the base component.
Ψ ∘ Φ = 1 on the vectors with coordinate sum zero.
The vectors with coordinate sum zero, times H_ab.
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W(P) ≅ {v : Σ v = 0} × G_ab (Proposition 7.2(1)).
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The vectors with coordinate sum zero are ℤ^{n−1}: forget the base coordinate.
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Proposition 7.2(1): W(P) ≅ ℤ^{n−1} ⊕ G_ab, with G the (free) deck group of the base
component and n the number of labels.
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θ_g = ζ(gx) − ζ(x) for every x of the base component, and under WPequivFree it is the
G_ab summand: g ↦ θ_g identifies G_ab with a direct summand with complement ℤ^{n−1}.
The identification W(P) = (I_𝓛)_G #
The base component 𝓛₀ of the lifted projective category.
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The deck action of G = H on 𝓛₀.
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The sum of coefficients.
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I_𝓛: finite sums with coefficient sum zero.
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The deck action on finite sums.
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The relations g·v − v of the coinvariants.
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The coinvariants (I_𝓛)_G.
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The values of ζ on finite sums.
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ζ(g o) − ζ(o) does not depend on o in the base component.
The comparison (I_𝓛)_G → W(P), [Σ v_o e_o] ↦ Σ v_o ζ(o).
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The base point of 𝓛₀.
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The chosen lift of a label in 𝓛₀.
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The generator e_o − e_{o₀} of I_𝓛.
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The class τ(g) = [e_{g o₀} − e_{o₀}].
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[e_{g b} − e_{o₀}] = [e_b − e_{o₀}] + τ(g).
τ is a homomorphism.
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The map ℤ^{labels} × G_ab → (I_𝓛)_G.
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The inverse comparison W(P) → (I_𝓛)_G.
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The class κ'(o) = o.2 · a_{o.1}⁻¹ ∈ G of an object of 𝓛₀.
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The identification W(P) = (I_𝓛)_G (Proposition 7.2(1)): [Σ v_o e_o] ↦ Σ v_o ζ(o),
for the base component 𝓛₀ and its deck group G.
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The identification on rays (Proposition 7.2(1)): the class of
e_{o'} − e_o = (e_{o'} − e_{o₀}) − (e_o − e_{o₀}) for a lifted ray o → o' corresponds to the
weight class of that ray.
The inverse direction of coinvEquiv_line: a lifted ray r : o → o' goes to [e_{o'} − e_o].