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CounterexampleConstruction: AI-generatedVerification: AI-generatedSession-authored (Fable 5 assisted)precheck passaudited 2026-08-11
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  • AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
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Omitting the absolute value from the Jacobian gives negative length under the reflection x1xx\mapsto1-x

Statement refuted

False claim. In the unoriented change-of-variables formula, one may replace φ|\varphi'| by φ\varphi'.

Facts & Assumptions

Counterexample

technique · direct
1.1

The image is [0,1][0,1], so its unoriented length integral is 011dy=1\int_0^1 1\,dy=1.

given
2.1

Since φ=1\varphi'=-1, the proposed un-absolute right side is 01(1)dx=1\int_0^1(-1)\,dx=-1, not 11.

givenstep 1.1
3.1

With the required absolute value, [L1] gives 011dx=1\int_0^1|-1|\,dx=1. The negative value in step 2.1 instead belongs to the oriented formula [L2], whose image endpoints occur in reverse order. Hence the claim is false.

L1L2step 2.1

Depends on

Used by

Nothing in the library uses this result yet.

Dependency tree · next 3 levels

Direct dependencies and their dependencies through the next three levels: 85 results over 18 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.