Proposition 4.14: descent of a multiplicative basis along a free deck group #
prop:scalar-normalization (scalar-normalization.tex): "Let b_{xy}
be the multiplicative basis constructed on L. For a free deck generator g,
write g(b_{xy}) = d_g(x, y) b_{gx,gy}. The coefficients form a multiplicative
weight. By Lemma 4.13, write d_g(x, y) = a_g(y)/a_g(x). On each orbit of
objects solve f(gx) = a_g(x) f(x) for all free generators. The orbit graph is a
Cayley tree, so a value at one root determines consistent values everywhere.
Then b'_{xy} = (f(y)/f(x)) b_{xy} is still multiplicative and is deck
invariant."
For a graded family with a thin cover, a multiplicative basis β on the cover,
a free grading group, and Lemma 4.13 as a hypothesis (hratio), we build the
deck-invariant multiplicative basis b' (invBasis). The deck group acts on
the cover by translating sheets (tr), with the same morphisms (trHom). The
values f are the transport of (root, 1) under the homomorphism from the free
group to permutations of objects × kˣ lifting the generators (Ψ): this is
"a value at one root determines consistent values everywhere".
Deck translations of the cover #
Translation of the sheet by g.
Instances For
The translated morphism (the same morphism of the family).
Instances For
Morphisms back from the translated objects.
Instances For
The weights d_g #
The coefficients of a deck translation: g(b_{xy}) = d_g(x, y) b_{gx,gy}.
Instances For
The coefficients form a multiplicative weight.
Object values on the orbits #
Lemma 4.13 applied to d_g: d_g(x, y) = a_g(y)/a_g(x).
The values a_g.
Instances For
The permutation of objects × kˣ lifting a free generator:
(o, λ) ↦ (g o, a_g(o) λ).
Instances For
The lift to the free group.
Instances For
The transports have the form (o, λ) ↦ (g o, c(o) λ).
Instances For
Induction over a free group.
The root of the orbit of o.
Instances For
The object values f: the transport of (root, 1).
Instances For
f(g x) = a_g(x) f(x) for the free generators.
The invariant basis #
b'_{xy} = (f(y)/f(x)) b_{xy}.
Instances For
The object (x, g) of the cover.
Instances For
b' is still multiplicative.
b' is invariant under the free generators.
b' is deck invariant.
Descent #
The descended vectors: b(x, y, g) = b'_{(x,1),(y,g)}.
Instances For
The descended vectors are multiplicative.