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TheoremStatement: Literature-sourcedProof: AI-adaptedPipeline-generatedverified 2026-09-26 (gpt-6-sol)
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The Plucker image is a closed projective algebraic set

Statement

The Plucker image of Gr⁡(r,V) is a closed projective algebraic set in P(ΛrV), cut out by the quadratic Plucker relations.

Facts & Assumptions

Given: Coordinates pI indexed by increasing r-subsets I of a basis of V. Extend the notation to any ordered r-tuple by declaring pi1…ir=0 for repeated indices and otherwise using the sign of the permutation that sorts the tuple.

Proof

1.1givenalgebra

For r=0 or r=n, the Grassmannian and P(ΛrV) are both one point, so the assertion is immediate. Suppose henceforth that 0<r<n. For ordered tuples (i1,…,ir−1) and (j1,…,jr+1), alternating multilinearity gives the signed Plucker relation ∑a=1r+1(−1)api1…ir−1japj1…ja^…jr+1=0. The ordered-coordinate convention supplies every insertion sign and makes repeated indices contribute zero.

2.1step 1.1algebra

On a chart with p1⋯r≠0, rescale so that p1⋯r=1 and define the entries of A by the coordinates with exactly one index outside {1,…,r}, using their alternating signs. The maximal minors of (Ir∣A) agree with these coordinates when zero or one index is outside the base set. Induct on the number of outside indices in an ordered r-tuple I. For an outside index j∈I, apply the relation of step 1.1 to the (r−1)-tuple I∖{j} and the (r+1)-tuple (1,…,r,j). The term omitting j is, up to sign, pIp1⋯r=pI; every other term is a product of a coordinate with fewer outside indices and a one-outside coordinate. The minors of (Ir∣A) satisfy the same relation, so the induction identifies pI with its corresponding minor. Thus the row span has precisely the given projective coordinates.

3.1step 2.1∎

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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