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Inter-universal Teichmuller Theory I: Construction of Hodge Theaters

Inter-universal Teichmuller Theory I: Construction of Hodge Theaters

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INTER-UNIVERSAL TEICHMÜLLER THEORY I 99<br />

That is to say, the portions <strong>of</strong> the diagram <strong>of</strong> Fig. 4.4 corresponding to † D > , † D ⊚<br />

differ quite fundamentally in structure. In particular, it is not surprising that the<br />

only “common ground” <strong>of</strong> these two fundamentally structurally different portions<br />

consists <strong>of</strong> an underlying set <strong>of</strong> cardinality l [i.e., the portion <strong>of</strong> the diagram <strong>of</strong><br />

Fig. 4.4 corresponding to † D J ].<br />

(iii) The bijection † ζ — or, perhaps more appropriately, its inverse<br />

( † ζ ) −1 : J ∼ → LabCusp( † D ⊚ )<br />

— may be thought <strong>of</strong> as relating arithmetic [i.e., if one thinks <strong>of</strong> the elements <strong>of</strong><br />

the capsule index set J as collections <strong>of</strong> primes <strong>of</strong> a number field] togeometry [i.e.,<br />

if one thinks <strong>of</strong> the elements <strong>of</strong> LabCusp( † D ⊚ ) as corresponding to the [geometric!]<br />

cusps <strong>of</strong> the hyperbolic orbicurve]. From this point <strong>of</strong> view,<br />

( † ζ ) −1 may be thought <strong>of</strong> as a sort <strong>of</strong> “combinatorial Kodaira-Spencer<br />

morphism” [cf. the point <strong>of</strong> view <strong>of</strong> [HASurI], §1.4].<br />

We refer to Remark 4.9.2, (iv), below, for another way to think about † ζ .<br />

[1< 2

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