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The Plucker image is a closed projective algebraic set
Statement
The Plucker image of is a closed projective algebraic set in , cut out by the quadratic Plucker relations.
Facts & Assumptions
Given: Coordinates indexed by increasing -subsets of a basis of . Extend the notation to any ordered -tuple by declaring for repeated indices and otherwise using the sign of the permutation that sorts the tuple.
Proof
For or , the Grassmannian and are both one point, so the assertion is immediate. Suppose henceforth that . For ordered tuples and , alternating multilinearity gives the signed Plucker relation The ordered-coordinate convention supplies every insertion sign and makes repeated indices contribute zero.
On the chart , divide by that coordinate and use the relations with to express every as the corresponding minor of the matrix . Its row span has precisely those coordinates.
The analogous charts cover every nonzero coordinate point satisfying the relations. Thus every such point is decomposable, while step 1.1 proved the reverse inclusion; homogeneous quadratic equations make this locus closed, and the injective Plucker map realizes it as the required projective algebraic set.
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Used by
Dependency tree · two levels
10 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- J. S. Milne, Algebraic Geometry, Proposition 6.29 and its second proof (standard reference, not scraped)
- MIT 18.725 Algebraic Geometry, Lecture 4, Theorem 4.1 (standard reference, not scraped)