Points of the toral Kostant closure #
The closed group scheme kostantToralGroupScheme is generated inside GLₙ by the represented
Kostant root subgroups together with the represented weight torus. This file identifies the
corresponding formal inclusion on algebra-valued points. Its point subgroup contains both the
pointwise elementary group and the represented torus, and hence contains their join.
For an arbitrary set S of root indices, write B_S(A) for the subgroup generated by the root
subgroups indexed by S and the torus. After passing from automorphisms of the base-changed
lattice to matrices in its chosen basis, the main theorem gives
B_S(A) ≤ kostantToralPointsSubgroup(A).
Taking S = Set.univ places the full torus--elementary subgroup assembled in
TauCeti.Algebra.Lie.UniversalEnveloping.Kostant.RootSubgroup.Borel inside the points
of the assembled scheme carrier. Equality over an algebraically closed field is a separate
generation theorem and is not asserted here.
Main declarations #
TauCeti.UniversalEnvelopingAlgebra.kostantToralPointsSubgroup: the algebra-valued points of the toral closure, viewed inGLₙ.TauCeti.UniversalEnvelopingAlgebra.kostantToralSchemePointMulEquiv: quotient-coordinate points of the toral closure identified with its scheme-valued points.TauCeti.UniversalEnvelopingAlgebra.kostantGeneratedPointsSubgroup_le_toralPoints: the root-generated point subgroup is contained in the toral point subgroup.TauCeti.UniversalEnvelopingAlgebra.kostantTorusMatrix_mem_toralPoints: every represented weight-torus point lies in the toral closure.TauCeti.UniversalEnvelopingAlgebra.kostantToralRootSubgroupPointsandTauCeti.UniversalEnvelopingAlgebra.kostantToralWeightTorusPoints: the canonical root-subgroup and weight-torus homomorphisms into the toral-closure points.TauCeti.UniversalEnvelopingAlgebra.kostantToralWeightTorusPoints_conj_rootSubgroupPoints: the pinning equation in those matrix-valued points.TauCeti.UniversalEnvelopingAlgebra.map_kostantTorusSubsystemSubgroup_le_toralPoints: every pointwise torus--root-subgroup join lies in the assembled scheme's points.
References #
The construction is the pointwise face of the split torus and root-subgroup carrier in the Chevalley--Demazure construction; see J. E. Humphreys, Linear Algebraic Groups, §26, and R. W. Carter, Simple Groups of Lie Type, §§4.4 and 7.1.
The algebra-valued points of the toral Kostant closure, embedded in GLₙ through its
Hopf-ideal quotient presentation.
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Instances For
The toral-closure points are the general-linear point subgroup cut out by the toral defining Hopf ideal.
Membership in the points of the toral closure is vanishing on its defining Hopf ideal.
The algebra-valued point subgroup of the toral closure contains the root-generated point subgroup: adjoining the weight torus to the generators enlarges the represented point subgroup (by shrinking the defining ideal).
Every represented weight-torus matrix is a point of the toral closure.
The canonical subgroups of the toral-closure points #
The canonical root-subgroup homomorphism into the matrix-valued points of the toral Kostant closure. The parameter is read through the multiplicative copy of the additive group.
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The canonical toral-closure root-subgroup point is its represented divided-power exponential matrix.
The canonical weight-torus homomorphism into the matrix-valued points of the toral Kostant closure.
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The canonical toral-closure weight-torus point is its diagonal weight matrix.
The integral-points presentation of the toral Kostant closure.
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- TauCeti.UniversalEnvelopingAlgebra.kostantToralPointsPresentation e h ρ M hM hnil b wt A = ⟨TauCeti.UniversalEnvelopingAlgebra.kostantToralPointsSubgroup e h ρ M hM hnil b wt A, ⋯⟩
Instances For
The presented toral-closure root point is natural in the value ring.
The presented toral-closure weight-torus point is natural in the value ring.
The pinning equation in the matrix-valued points of the toral Kostant closure. If e i has
Cartan weight α, conjugation by the weight-torus point s rescales the root-subgroup
parameter by α(s). This is not a simp lemma: the weight α is pinned only by the hypothesis
hα, so simp could never infer it from the left-hand side.
After writing automorphisms in the basis b, every subgroup generated by a set of represented
root subgroups together with the weight torus lies in the points of the toral closure.
Scheme-valued points #
The toral closure is represented by its quotient coordinate Hopf algebra.
The underlying scheme of the toral closure is the spectrum of its coordinate ring.
Algebra-valued points of the toral closure, transported to scheme-valued points.
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The underlying spectrum map of a quotient point of the toral closure.