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SpherePacking.MagicFunction.IntegralParametrisations

Integral Parametrisations #

Parametrisations of the contours used to define the magic-function integrals.

theorem MagicFunction.Parametrisations.neg_inv_eq_S (z : UpperHalfPlane) :
{ coe := -1 / ↑z, coe_im_pos := ⋯ } = ModularGroup.S • z

The Möbius map w ↦ -1/w sends the upper-half-plane set ℍ₀ ⊆ ℂ to itself. (Set-level analogue of neg_inv_mem, which is stated for the subtype ℍ.)

For a real shift c (c.im = 0), z ↦ -1/(z + c) maps ℍ₀ into ℍ₀.