Pointwise operations on filters #
This file defines pointwise operations on filters. This is useful because usual algebraic operations distribute over pointwise operations. For example,
(f₁ * f₂).map m = f₁.map m * f₂.map m𝓝 (x * y) = 𝓝 x * 𝓝 y
Main declarations #
0(Filter.instZero): Pure filter at0 : α, or alternatively principal filter at0 : Set α.1(Filter.instOne): Pure filter at1 : α, or alternatively principal filter at1 : Set α.f + g(Filter.instAdd): Addition, filter generated by alls + twheres ∈ fandt ∈ g.f * g(Filter.instMul): Multiplication, filter generated by alls * twheres ∈ fandt ∈ g.-f(Filter.instNeg): Negation, filter of all-swheres ∈ f.f⁻¹(Filter.instInv): Inversion, filter of alls⁻¹wheres ∈ f.f - g(Filter.instSub): Subtraction, filter generated by alls - twheres ∈ fandt ∈ g.f / g(Filter.instDiv): Division, filter generated by alls / twheres ∈ fandt ∈ g.f +ᵥ g(Filter.instVAdd): Scalar addition, filter generated by alls +ᵥ twheres ∈ fandt ∈ g.f -ᵥ g(Filter.instVSub): Scalar subtraction, filter generated by alls -ᵥ twheres ∈ fandt ∈ g.f • g(Filter.instSMul): Scalar multiplication, filter generated by alls • twheres ∈ fandt ∈ g.a +ᵥ f(Filter.instVAddFilter): Translation, filter of alla +ᵥ swheres ∈ f.a • f(Filter.instSMulFilter): Scaling, filter of alla • swheres ∈ f.
For α a semigroup/monoid, Filter α is a semigroup/monoid.
As an unfortunate side effect, this means that n • f, where n : ℕ, is ambiguous between
pointwise scaling and repeated pointwise addition. See note [pointwise nat action].
Implementation notes #
We put all instances in the locale Pointwise, so that these instances are not available by
default. Note that we do not mark them as reducible (as argued by note [reducible non-instances])
since we expect the locale to be open whenever the instances are actually used (and making the
instances reducible changes the behavior of simp).
Tags #
filter multiplication, filter addition, pointwise addition, pointwise multiplication,
0/1 as filters #
1 : Filter α is defined as the filter of sets containing 1 : α in locale Pointwise.
Equations
- Filter.instOne = { one := pure 1 }
Instances For
0 : Filter α is defined as the filter of sets containing 0 : α in locale Pointwise.
Equations
- Filter.instZero = { zero := pure 0 }
Instances For
Filter negation/inversion #
The inverse of a filter is the pointwise preimage under ⁻¹ of its sets.
Equations
- Filter.instInv = { inv := Filter.map Inv.inv }
The negation of a filter is the pointwise preimage under - of its sets.
Equations
- Filter.instNeg = { neg := Filter.map Neg.neg }
Filter addition/multiplication #
pure operation as a MulHom.
Equations
- Filter.pureMulHom = { toFun := pure, map_mul' := ⋯ }
Instances For
The singleton operation as an AddHom.
Equations
- Filter.pureAddHom = { toFun := pure, map_add' := ⋯ }
Instances For
Filter subtraction/division #
Repeated pointwise multiplication/division (not the same as pointwise repeated
multiplication/division!) of a Filter. See Note [pointwise nat action].
Instances For
If φ : α →* β then mapMonoidHom φ is the monoid homomorphism
Filter α →* Filter β induced by map φ.
Equations
- Filter.mapMonoidHom φ = { toFun := Filter.map ⇑φ, map_one' := ⋯, map_mul' := ⋯ }
Instances For
If φ : α →+ β then mapAddMonoidHom φ is the monoid homomorphism
Filter α →+ Filter β induced by map φ.
Equations
- Filter.mapAddMonoidHom φ = { toFun := Filter.map ⇑φ, map_zero' := ⋯, map_add' := ⋯ }
Instances For
pure as a MonoidHom.
Equations
- Filter.pureMonoidHom = { toFun := Filter.pureMulHom.toFun, map_one' := ⋯, map_mul' := ⋯ }
Instances For
pure as an AddMonoidHom.
Equations
- Filter.pureAddMonoidHom = { toFun := Filter.pureAddHom.toFun, map_zero' := ⋯, map_add' := ⋯ }
Instances For
Filter α is a Monoid under pointwise operations if α is.
Equations
- Filter.monoid = Monoid.mk ⋯ ⋯ npowRecAuto ⋯ ⋯
Instances For
Filter α is an AddMonoid under pointwise operations if α is.
Equations
- Filter.addMonoid = AddMonoid.mk ⋯ ⋯ nsmulRecAuto ⋯ ⋯
Instances For
Filter α is a commutative subtraction monoid under pointwise operations if α is.
Instances For
Note that Filter is not a MulZeroClass because 0 * ⊥ ≠ 0.
Note that Filter α is not a group because f / f ≠ 1 in general
Scalar addition/multiplication of filters #
Scalar subtraction of filters #
Translation/scaling of filters #
a • f is the map of f under a • in locale Pointwise.
Equations
- Filter.instSMulFilter = { smul := fun (a : α) => Filter.map fun (x : β) => a • x }
Instances For
a +ᵥ f is the map of f under a +ᵥ in locale Pointwise.
Equations
- Filter.instVAddFilter = { vadd := fun (a : α) => Filter.map fun (x : β) => a +ᵥ x }
Instances For
A distributive multiplicative action of a monoid on an additive monoid β gives a distributive
multiplicative action on Filter β.
Equations
Instances For
A multiplicative action of a monoid on a monoid β gives a multiplicative action on Set β.
Equations
Instances For
Note that we have neither SMulWithZero α (Filter β) nor SMulWithZero (Filter α) (Filter β)
because 0 * ⊥ ≠ 0.