Inter-universal Teichmuller Theory I: Construction of Hodge Theaters

Inter-universal Teichmuller Theory I: Construction of Hodge Theaters Inter-universal Teichmuller Theory I: Construction of Hodge Theaters

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96 SHINICHI MOCHIZUKI Definition 4.6. (i) We define a base-NF-bridge, orD-NF-bridge, [relative to the given initial Θ-data] to be a poly-morphism † † φ NF D J −→ † D ⊚ —where † D ⊚ is a category equivalent to D ⊚ ; † D J = { † D j } j∈J is a capsule of D- prime-strips, indexed by a finite index set J — such that there exist isomorphisms D ⊚ → ∼ † D ⊚ ∼ , D → † D J , conjugation by which maps φ NF ↦→ † φ NF . We define a(n) [iso]morphism of D-NF-bridges to be a pair of poly-morphisms ( † † φ NF D J −→ † D ⊚ ) → ( ‡ D J ′ ‡ φ NF −→ ‡ D ⊚ ) † D J ∼ → ‡ D J ′; † D ⊚ ∼ → ‡ D ⊚ —where † ∼ D J → ‡ D J ′ is a capsule-full poly-isomorphism [cf. §0]; † D ⊚ → ‡ D ⊚ is a poly-morphism which is an Aut ɛ ( † D ⊚ )- [or, equivalently, Aut ɛ ( ‡ D ⊚ )-] orbit [cf. the discussion of Example 4.3, (i)] of isomorphisms — which are compatible with † φ NF ‡ φ NF . There is an evident notion of composition of morphisms of D-NF-bridges. (ii) We define a base-Θ-bridge, or D-Θ-bridge, [relative to the given initial Θ-data] to be a poly-morphism † † φ Θ D J −→ † D > —where † D > is a D-prime-strip; † D J = { † D j } j∈J is a capsule of D-prime-strips, ∼ indexed by a finite index set J — such that there exist isomorphisms D > → † D > , ∼ → † D J , conjugation by which maps φ Θ ↦→ † φ Θ . We define a(n) [iso]morphism D of D-Θ-bridges , ( † † φ Θ D J −→ † D > ) → ( ‡ D J ′ ‡ φ Θ −→ ‡ D > ) to be a pair of poly-morphisms † D J ∼ → ‡ D J ′; † D > ∼ → ‡ D > —where † ∼ D J → ‡ D J ′ is a capsule-full poly-isomorphism; † ∼ D > → ‡ D > is the full poly-isomorphism — which are compatible with † φ Θ , ‡ φ Θ . There is an evident notion of composition of morphisms of D-Θ-bridges. (iii) We define a base-ΘNF-Hodge theater, orD-ΘNF-Hodge theater, [relative to the given initial Θ-data] to be a collection of data † HT D-ΘNF =( † D ⊚ † φ NF ←− † † φ Θ D J −→ † D > ) —where † φ NF isomorphisms is a D-NF-bridge; † φ Θ is a D-Θ-bridge — such that there exist D ⊚ ∼ → † D ⊚ ; D ∼ → † D J ; D > ∼ → † D >

conjugation by which maps φ NF INTER-UNIVERSAL TEICHMÜLLER THEORY I 97 ↦→ † φ NF , φ Θ ↦→ † φ Θ . A(n) [iso]morphism of D- ΘNF-Hodge theaters is defined to be a pair of morphisms between the respective associated D-NF- and D-Θ-bridges that are compatible with one another in the sense that they induce the same bijection between the index sets of the respective capsules of D-prime-strips. There is an evident notion of composition of morphisms of D-ΘNF-Hodge theaters. Proposition 4.7. Bridges) Let (Transport of Label Classes of Cusps via Base- † HT D-ΘNF =( † D ⊚ † φ NF ←− † † φ Θ D J −→ † D > ) be a D-ΘNF-Hodge theater [relative to the given initial Θ-data]. Then: (i) The structure at the v ∈ V bad of the D-Θ-bridge † φ Θ determines a bijection † χ : π 0 ( † D J )=J ∼ → F l — i.e., determines labels ∈ F l for the constituent D-prime-strips of the capsule † D J . (ii) For each j ∈ J, restriction at the various v ∈ V [cf. Example 4.5] via the portion of † φ NF , † φ Θ indexed by j determines an isomorphism of F l -torsors † φ LC j : LabCusp( † D ⊚ ) ∼ → LabCusp( † D > ) such that † φ LC j is obtained from † φ LC 1 [where, by abuse of notation, we write “1 ∈ J” for the element of J that maps via † χ to the image of 1 in F l ] by composing with the action by † χ(j) ∈ F l . (iii) There exists a unique element [ † ɛ] ∈ LabCusp( † D ⊚ ) such that for each j ∈ J, the natural bijection LabCusp( † D > ) → ∼ F l of the second display of Proposition 4.2 maps † φ LC j ([ † ɛ]) = † φ LC 1 ( † χ(j) · [ † ɛ]) ↦→ † χ(j). In particular, the element [ † ɛ] determines an isomorphism of F l -torsors † ζ : LabCusp( † D ⊚ ) ∼ → J ( ∼ → F l ) [where the bijection in parentheses is the bijection † χ of (i)] between “global cusps” [i.e., “ † χ(j) · [ † ɛ]”] and capsule indices [i.e., j ∈ J → ∼ F l ]. Finally, when considered up to composition with multiplication by an element of F l ,the bijection † ζ is independent of the choice of † φ NF within the F l -orbit of † φ NF relative to the natural poly-action of F l on † D ⊚ [cf. Example 4.3, (iii); Fig. 4.4 below]. Proof. Assertion (i) follows immediately from the definitions [cf. Example 4.4, (i), (ii), (iv); Definition 4.6], together with the bijection of the second display of

96 SHINICHI MOCHIZUKI<br />

Definition 4.6.<br />

(i) We define a base-NF-bridge, orD-NF-bridge, [relative to the given initial<br />

Θ-data] to be a poly-morphism<br />

† † φ NF<br />

<br />

D J −→<br />

† D ⊚<br />

—where † D ⊚ is a category equivalent to D ⊚ ; † D J = { † D j } j∈J is a capsule <strong>of</strong> D-<br />

prime-strips, indexed by a finite index set J — such that there exist isomorphisms<br />

D ⊚ → ∼ † D ⊚ ∼<br />

, D → † D J , conjugation by which maps φ NF<br />

↦→ † φ NF<br />

. We define a(n)<br />

[iso]morphism <strong>of</strong> D-NF-bridges<br />

to be a pair <strong>of</strong> poly-morphisms<br />

( † † φ NF<br />

<br />

D J −→ † D ⊚ ) → ( ‡ D J ′<br />

‡ φ NF<br />

<br />

−→ ‡ D ⊚ )<br />

† D J<br />

∼<br />

→ ‡ D J ′;<br />

† D ⊚ ∼<br />

→ ‡ D ⊚<br />

—where † ∼<br />

D J → ‡ D J<br />

′ is a capsule-full poly-isomorphism [cf. §0]; † D ⊚ → ‡ D ⊚ is a<br />

poly-morphism which is an Aut ɛ ( † D ⊚ )- [or, equivalently, Aut ɛ ( ‡ D ⊚ )-] orbit [cf. the<br />

discussion <strong>of</strong> Example 4.3, (i)] <strong>of</strong> isomorphisms — which are compatible with † φ NF<br />

‡ φ NF<br />

<br />

. There is an evident notion <strong>of</strong> composition <strong>of</strong> morphisms <strong>of</strong> D-NF-bridges.<br />

(ii) We define a base-Θ-bridge, or D-Θ-bridge, [relative to the given initial<br />

Θ-data] to be a poly-morphism<br />

† † φ Θ <br />

D J −→ † D ><br />

—where † D > is a D-prime-strip; † D J = { † D j } j∈J is a capsule <strong>of</strong> D-prime-strips,<br />

∼<br />

indexed by a finite index set J — such that there exist isomorphisms D > → † D > ,<br />

∼<br />

→ † D J , conjugation by which maps φ Θ ↦→ † φ Θ . We define a(n) [iso]morphism<br />

D <br />

<strong>of</strong> D-Θ-bridges<br />

,<br />

( † † φ Θ <br />

D J −→ † D > ) → ( ‡ D J ′<br />

‡ φ Θ <br />

−→ ‡ D > )<br />

to be a pair <strong>of</strong> poly-morphisms<br />

† D J<br />

∼<br />

→ ‡ D J ′;<br />

† D ><br />

∼<br />

→ ‡ D ><br />

—where † ∼<br />

D J → ‡ D J ′ is a capsule-full poly-isomorphism; † ∼<br />

D > → ‡ D > is the full<br />

poly-isomorphism — which are compatible with † φ Θ , ‡ φ Θ . There is an evident<br />

notion <strong>of</strong> composition <strong>of</strong> morphisms <strong>of</strong> D-Θ-bridges.<br />

(iii) We define a base-ΘNF-<strong>Hodge</strong> theater, orD-ΘNF-<strong>Hodge</strong> theater, [relative<br />

to the given initial Θ-data] to be a collection <strong>of</strong> data<br />

† HT D-ΘNF =( † D ⊚ † φ NF<br />

<br />

←− † † φ Θ <br />

D J −→ † D > )<br />

—where † φ NF<br />

<br />

isomorphisms<br />

is a D-NF-bridge; † φ Θ is a D-Θ-bridge — such that there exist<br />

D ⊚ ∼<br />

→ † D ⊚ ; D <br />

∼<br />

→ † D J ; D ><br />

∼<br />

→ † D >

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