How statement and proof provenance work
The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
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The Borel and Cartan cohomology of a point
Example
Assume AC and let act trivially on the one-point smooth manifold . Use the period-one tangent generator and its selected degree-two polynomial generator . In the chosen Borel model, , with . The Cartan complex is with zero differential, so its cohomology is also under the selected coefficient normalization.
Example references
[Borel and Cartan definitions and cohomology of a point] Borel and Cartan equivariant cohomology for a compact torus
[Torus classifying-space coefficient ring] Real cohomology of the chosen torus classifying space
[Smooth differential forms] A smooth differential -form
Facts & Assumptions
Given: AC, the rank-one torus , its trivial action on , and the degree-two normalization fixed in the A-page definition.
Assume the Axiom of Choice, as required by the selected coefficient-ring and Cartan definitions. The Axiom of Choice
The Borel construction and Cartan complex use the selected product Milnor model; the Cartan polynomial generators have degree two. Borel and Cartan equivariant cohomology for a compact torus
The selected coefficient identification sends the period-one Lie-algebra dual generator to and gives . Real cohomology of the chosen torus classifying space
Smooth differential -forms are sections of the exterior powers of the cotangent bundle. A smooth differential -form
Proof
Since the action on the point is trivial, by the Borel definition [F1]. Its singular cohomology ring is by [F2].
The tangent and cotangent spaces of a point are zero. Every real-valued function on the singleton is constant, so [F3] gives ; for , the th exterior power of its zero cotangent space is zero, hence . Every fundamental field is zero and the exterior derivative of a constant function is zero. Thus the Cartan complex is with zero differential, whose cohomology ring is .
Both presentations use the degree-two generator fixed in [F2], so the displayed rings agree under that normalization. The example asserts no comparison for other -manifolds.