Drinfeld upper half plane

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In

upper half plane for function fields, introduced by Drinfeld (1976
). It is defined to be P1(C)\P1(F), where F is a function field of a curve over a finite field, F its completion at ∞, and C the completion of the algebraic closure of F.

The analogy with the usual upper half plane arises from the fact that the

global function field F is analogous to the rational numbers Q. Then, F is the real numbers R and the algebraic closure of F is the complex numbers C (which are already complete). Finally, P1(C) is the Riemann sphere
, so P1(C)\P1(R) is the upper half plane together with the lower half plane.

References