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Mathlib.Topology.ContinuousMap.ZeroAtInftyUnitization

The unitization (over R) of C₀(X, R) is C(OnePoint X, R) #

Given a topological space X and a topological ring R one can extend an element C₀(X, R), the continuous functions vanishing at infinity, to C(OnePoint X, R), the continuous functions on the one-point compactification of X, by taking the value 0 at . This can be lifted to an equivalence between Unitization R C₀(X, R) and C(OnePoint X, R).

Main definitions #

Implementation notes #

The simp normal form of each bundled morphism is the unbundled map, so the unbundled maps have their own simp lemmas for various operatoins.

Extension by zero of a continuous function vanishing at infinity, as a continuous function on the one-point compactification.

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    The continuous function vanishing at infinity obtained by taking g : C(OnePoint X, R) and restricting g to X and subtracting the constant g ∞.

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      The canonical equivalence Unitization R C₀(X, R) ≃ C(OnePoint X, R) mapping (r, f) to the function taking the value r at and r + f x at x : X. Its inverse maps g to (g ∞, fun x ↦ g x - g ∞). This is the lift of ZeroAtInftyContinuousMap.toOnePoint.

      Various bundlings are available including unitizationAddEquiv, unitizationLinearEquiv, unitizationRingEquiv, unitizationAlgEquiv, unitizationStarAlgEquiv.

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        ZeroAtInftyContinuousMap.unitizationEquiv as a LinearEquiv.

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