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Levine–Weibel cycle image with pure-dimensional and component conventions

PDF p. 3: Levine–Weibel image after TheoremC; PDF p. 14: Definition6.5 pure-dimensional smooth-point subgroup

Remark

Assume AC and the completed size conventions. In the article's pure-dimensional normal affine finite-type threefold setting over an algebraically closed field, im⁡(cyc⁡X:CH⁡0LW(X)→K0(X))=Fsm3K0(X). The map sends [x] to the actual perfect residue-sheaf class [i∗κ(x)]=φx(1) and kills the specified Cartier-curve principal-divisor relations. Thus it is a surjection onto this image subgroup; no injectivity or identification of the whole Chow group with its image is asserted. The pure-dimensional interpretation is explicit in the source Definition6.5, so it does not require treating the customary word threefold/variety as an original-paper error.

For a normal affine finite-type scheme of dimension three over the same field with lower-dimensional clopen components, put X3 for the union of its three-dimensional components. The exact source dimension-three convention gives the stronger, unambiguous componentwise formula CH⁡Kr3(X)≅CH⁡0LW(X3),im⁡(cyc⁡XKr)=Fsm,top3K0(X)=(i3)∗Fsm3K0(X3)⊆Fmot3K0(X). Here Fsm,top3 is the zero-extended top-dimensional point image defined and justified in the local prerequisite. Lower-dimensional strata have their own same-dimension Levine–Weibel point images (and a free weight-zero point group in dimension zero). The subgroup generated by all geometrically smooth closed points across these strata is their direct sum; it is not in general a subgroup of weight three. The explicit A3⨿Spec⁡k counterexample prevents that overbroad generated interpretation. None of these clarifications edits the completed pure-dimensional definitions.

Facts & Assumptions

Given: The field and finite-type scheme hypotheses just stated, the actual point-map normalization and the completed definitions. These finite-type hypotheses agree with the article’s affine convention on printed p. 3.

Goal: Establish the source remark's image claim, its quotient-map premise, and the strongest correct nonpure componentwise form.

[F1]

External Levine–Weibel quotient cycle map with exact generators supplies the source-backed quotient map, actual point values and relation-vanishing.

[F3]

The quotient cycle map has exactly the smooth-point image proves the image equality on pure pieces; Dimension-specific point images and a precise lower-component obstruction proves the top-dimensional formula and the lower-component obstruction.

Proof

1.1F1F2F3given

In the pure-dimensional threefold case, affineness and finite type give quasi-projectivity and normality gives reducedness; the algebraically closed field is perfect. Thus apply [F1] with d=3. By [F2] its generator [κ(x)] is the current class φx(1), and its relation subgroup is the completed Levine–Weibel one. Since the quotient map from the free point group is surjective, the cycle map has the same image as the free point-class homomorphism. By [F3] that image is precisely Fsm3K0(X), proving the first displayed equality with its actual factorization.

2.1F1F2F3step 1.1∎

In the dimension-only nonpure normal case, [F2] identifies Krishna's top-dimensional quotient with the pure X3 quotient, and identifies the actual K-map with zero extension from that piece. The clopen scheme X3 remains affine and finite type over the same field, so apply step 1.1 to X3 and the filtered product result in [F2] to obtain the second display. The dimension-specific direct-sum statement and its counterexample are exactly [F3]. Thus both the source pure theorem and its precise broader componentwise formulation are established, without adding a false fixed-weight assertion about smaller components or inferring a published defect from a conventional purity assumption.

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