Lemma A.1(1) for an arbitrary rooted tree #
lem:periodic-scalar-gauges (1), periodic-mesh-calculations.tex: "Let
Q = ℤΔ/⟨τ^s ρ⟩, where Δ is a finite tree oriented away from a root fixed by ρ. Every
nonzero coefficient system c can be changed to the signed preprojective coefficients."
Proof: "Label the arrows over a parent-child edge orbit […] Such labels can be assigned
recursively down the rooted orbit tree. […] Dividing the two equations gives a recurrence for
μ_a. It closes around the cycle exactly when [a product of the η] equals a prescribed number.
Choose the root product freely and assign the child products down the tree. Realize each product
by one factor, setting the other factors to one."
The rooted tree is given by a parent map pa reaching the root o (Rooted), and the twist
σ fixes o and commutes with pa. For each vertex v ≠ o the edge line {v, pa v} is solved
on the representative rep v of the σ-orbit of v, with period per v · c₀, from the relation
scales of its parent (step, exists_periodic_line_vertex), and transported along the orbit; the
recursion runs on the depth (NM). The solution is g-invariant and solves every edge equation
(main). The star version is StarGauge.exists_signed_gauge.
The depth: the number of parent steps to the root.
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The edge lines #
The prescribed products on the edge line {v, pa v}, given the relation scales Np of the
parent.
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One edge: the child's relation scales and the edge's arrow scales.
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The scales, recursively down the tree: at v ≠ o, the relation scales of v and the
arrow scales of the edge {v, pa v}, solved on the orbit representative and transported.
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The relation scales.
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The arrow scales of the edge {v, pa v}.
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The step on the representative of v.
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Invariance and the edge equations #
One-step invariance iterates.
The scales are g-invariant and solve the edge equations, by induction on the depth.
The coefficients of Q along the covering #
The coefficient of Q at π (w, h + 2) of the image of the arrow from (w', h + 1).
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The endpoint of an edge further from the root.
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The relation scales and arrow scales on ℤΔ.
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The gauge equations on ℤΔ.
Descent to Q #
The relation scale at a vertex of ℤΔ.
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The arrow scale of the arrow Y → X of ℤΔ.
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Arrows into a vertex of ℤΔ are determined by the image of their source.
The relation scales on Q.
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The arrow scales on Q.
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Lemma A.1(1) (lem:periodic-scalar-gauges), for an arbitrary finite tree Δ
oriented away from a root o fixed by the twist σ: for a covering π : ℤΔ → Q commuting
with translation whose fibres are the orbits of g (v, t) = (σ v, t + c₀), rescaling arrows and
entire mesh relations of Q turns every coefficient system into the signed preprojective
coefficients.
Lemma A.1(1), without an auxiliary order on the vertices.