The bundle of alternating maps between C^n vector bundles over the same base space is C^n #
Here we show that the bundle of continuous alternating linear maps is a C^n vector bundle,
when the base field has characteristic zero.
We also show that applying a smooth family of alternating maps to smooth families of vectors gives a smooth result, in several versions.
Note that, in positive characteristic, the result is true in finite dimension, but not in
general for n = ฯ.
See https://leanprover.zulipchat.com/#narrow/channel/287929-mathlib4/topic/bundles.20of.20alternating.20maps/near/630597041
For now, we only implement the characteristic zero case as it is the most important.
Consider C^n maps vโ, ..., vแตข : M โ Eโ to a vector bundle, over a base map bโ : M โ Bโ,
and another base map bโ : M โ Bโ. Given alternating maps ฯ m : Eโ (bโ m) [โ^ฮน]โL[๐] Eโ (bโ m)
depending smoothly on m, one can apply ฯ m to (vโ m, ..., vแตข m), and the
resulting map is C^n.
Note that the smoothness of ฯ cannot always be stated as smoothness of a map into a manifold,
as the pullback bundles bโ *แต Eโ and bโ *แต Eโ are smooth manifolds only when bโ and bโ are
globally smooth, but we want to apply this lemma with only local information. Therefore, we
formulate it using smoothness of ฯ read in coordinates.
Version for ContMDiffWithinAt. We also give a version for ContMDiffAt, but no version for
ContMDiffOn or ContMDiff as our assumption, written in coordinates, only makes sense around
a point.
For a version with Bโ = Bโ and bโ = bโ, in which smoothness can be expressed without
inCoordinates, see ContMDiffWithinAt.continuousAlternatingMap_bundle_apply.
Consider a C^n map v : M โ Eโ to a vector bundle, over a base map bโ : M โ Bโ, and
another base map bโ : M โ Bโ. Given linear maps ฯ m : Eโ (bโ m) โ Eโ (bโ m) depending smoothly
on m, one can apply ฯ m to v m, and the resulting map is C^n.
Note that the smoothness of ฯ cannot always be stated as smoothness of a map into a manifold,
as the pullback bundles bโ *แต Eโ and bโ *แต Eโ are smooth manifolds only when bโ and bโ are
globally smooth, but we want to apply this lemma with only local information. Therefore, we
formulate it using smoothness of ฯ read in coordinates.
Version for ContMDiffAt. We also give a version for ContMDiffWithinAt, but no version for
ContMDiffOn or ContMDiff as our assumption, written in coordinates, only makes sense around
a point.
For a version with Bโ = Bโ and bโ = bโ, in which smoothness can be expressed without
inCoordinates, see ContMDiffAt.continuousAlternatingMap_bundle_apply.
Consider differentiable maps vโ, ..., vแตข : M โ Eโ to a vector bundle, over a base
map bโ : M โ Bโ, and another base map bโ : M โ Bโ. Given alternating maps
ฯ m : Eโ (bโ m) [โ^ฮน]โL[๐] Eโ (bโ m) depending differentiably on m, one can
apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is differentiable.
Note that the differentiability of ฯ cannot always be stated as differentiability of a map into
a manifold, as the pullback bundles bโ *แต Eโ and bโ *แต Eโ are smooth manifolds only
when bโ and bโ are globally smooth, but we want to apply this lemma with only local information.
Therefore, we formulate it using differentiability of ฯ read in coordinates.
Version for MDifferentiableWithinAt. We also give a version for MDifferentiableAt, but no
version for MDifferentiableOn or MDifferentiable as our assumption, written in coordinates,
only makes sense around a point.
For a version with Bโ = Bโ and bโ = bโ, in which smoothness can be expressed without
inCoordinates, see MDifferentiableWithinAt.continuousAlternatingMap_bundle_apply.
Consider differentiable maps vโ, ..., vแตข : M โ Eโ to a vector bundle, over a base
map bโ : M โ Bโ, and another base map bโ : M โ Bโ. Given alternating maps
ฯ m : Eโ (bโ m) [โ^ฮน]โL[๐] Eโ (bโ m) depending differentiably on m, one can
apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is differentiable.
Note that the differentiability of ฯ cannot always be stated as differentiability of a map into
a manifold, as the pullback bundles bโ *แต Eโ and bโ *แต Eโ are smooth manifolds only
when bโ and bโ are globally smooth, but we want to apply this lemma with only local information.
Therefore, we formulate it using differentiability of ฯ read in coordinates.
Version for MDifferentiableAt. We also give a version for MDifferentiableWithinAt, but no
version for MDifferentiableOn or MDifferentiable as our assumption, written in coordinates,
only makes sense around a point.
For a version with Bโ = Bโ and bโ = bโ, in which smoothness can be expressed without
inCoordinates, see MDifferentiableAt.continuousAlternatingMap_bundle_apply.
Consider C^n maps vแตข : M โ Eโ to a vector bundle, over a base map b : M โ B, and
alternating linear maps ฯ m : Eโ (b m) [โ^ฮน]โ Eโ (b m) depending smoothly on m.
One can apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is C^n.
We give here a version of this statement within a set at a point.
Consider C^n maps vแตข : M โ Eโ to a vector bundle, over a base map b : M โ B, and
alternating linear maps ฯ m : Eโ (b m) [โ^ฮน]โ Eโ (b m) depending smoothly on m.
One can apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is C^n.
We give here a version of this statement at a point.
Consider C^n maps vแตข : M โ Eโ to a vector bundle, over a base map b : M โ B, and
alternating linear maps ฯ m : Eโ (b m) [โ^ฮน]โ Eโ (b m) depending smoothly on m.
One can apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is C^n.
We give here a version of this statement on a set.
Consider C^n maps vแตข : M โ Eโ to a vector bundle, over a base map b : M โ B, and
alternating linear maps ฯ m : Eโ (b m) [โ^ฮน]โ Eโ (b m) depending smoothly on m.
One can apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is C^n.
Consider differentiable maps vแตข : M โ Eโ to a vector bundle, over a base map b : M โ B, and
alternating linear maps ฯ m : Eโ (b m) [โ^ฮน]โ Eโ (b m) depending differentiably on m.
One can apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is differentiable.
We give here a version of this statement within a set at a point.
Consider differentiable maps vแตข : M โ Eโ to a vector bundle, over a base map b : M โ B, and
alternating linear maps ฯ m : Eโ (b m) [โ^ฮน]โ Eโ (b m) depending differentiably on m.
One can apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is differentiable.
We give here a version of this statement at a point.
Consider differentiable maps vแตข : M โ Eโ to a vector bundle, over a base map b : M โ B, and
alternating linear maps ฯ m : Eโ (b m) [โ^ฮน]โ Eโ (b m) depending differentiably on m.
One can apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is differentiable.
We give here a version of this statement on a set.
Consider differentiable maps vแตข : M โ Eโ to a vector bundle, over a base map b : M โ B, and
alternating linear maps ฯ m : Eโ (b m) [โ^ฮน]โ Eโ (b m) depending differentiably on m.
One can apply ฯ m to (vโ m, ..., vแตข m), and the resulting map is differentiable.