Alphabeta Math
ExampleConstruction: AI-generatedVerification: Not suppliedSession-authored (Fable 5 assisted)judge pass (z-ai/glm-5.2)audited 2026-07-31
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Under choice and dependent choice, a finite subordinate partition of unity for a two-set cover of a compact interval

Example

On [0,1][0,1], take the open-in-the-subspace cover U=(1,34)[0,1]U=(-1,\tfrac34)\cap[0,1] and V=(14,2)[0,1]V=(\tfrac14,2)\cap[0,1]. Define φ(x)=max{0,min{1,23x}},ψ(x)=1φ(x).\varphi(x)=\max\{0,\min\{1,2-3x\}\},\qquad\psi(x)=1-\varphi(x). Then φ\varphi and ψ\psi are continuous, nonnegative, and sum to one. Their supports are contained respectively in [0,23]U[0,\tfrac23]\subseteq U and [13,1]V[\tfrac13,1]\subseteq V, so they are a finite subordinate partition of unity.

The explicit pair is an instance of the existence theorem Under choice and dependent choice, every open cover of a compact Hausdorff space admits a finite subordinate partition of unity, under its stated Choice and Dependent Choice hypotheses.

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Dependency tree · next 3 levels

Direct dependencies and their dependencies through the next three levels: 58 results over 16 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.

Sources