Germ of a function at a filter #
The germ of a function f : α → β at a filter l : Filter α is the equivalence class of f
with respect to the equivalence relation EventuallyEq l: f ≈ g means ∀ᶠ x in l, f x = g x.
Main definitions #
We define
Filter.Germ l βto be the space of germs of functionsα → βat a filterl : Filter α;- coercion from
α → βtoGerm l β:(f : Germ l β)is the germ off : α → βatl : Filter α; this coercion is declared asCoeTC; (const l c : Germ l β)is the germ of the constant functionfun x : α ↦ cat a filterl;- coercion from
βtoGerm l β:(↑c : Germ l β)is the germ of the constant functionfun x : α ↦ cat a filterl; this coercion is declared asCoeTC; map (F : β → γ) (f : Germ l β)to be the composition of a functionFand a germf;map₂ (F : β → γ → δ) (f : Germ l β) (g : Germ l γ)to be the germ offun x ↦ F (f x) (g x)atl;f.Tendsto lb: we say that a germf : Germ l βtends to a filterlbif its representatives tend tolbalongl;f.compTendsto g hgandf.compTendsto' g hg: givenf : Germ l βand a functiong : γ → α(resp., a germg : Germ lc α), ifgtends tolalonglc, then the compositionf ∘ gis a well-defined germ atlc;Germ.liftPred,Germ.liftRel: lift a predicate or a relation to the space of germs:(f : Germ l β).liftPred pmeans∀ᶠ x in l, p (f x), and similarly for a relation.
We also define map (F : β → γ) : Germ l β → Germ l γ sending each germ f to F ∘ f.
For each of the following structures we prove that if β has this structure, then so does
Germ l β:
- one-operation algebraic structures up to
CommGroup; MulZeroClass,Distrib,Semiring,CommSemiring,Ring,CommRing;MulAction,DistribMulAction,Module;Preorder,PartialOrder, andLatticestructures, as well asBoundedOrder;
Tags #
filter, germ
Setoid used to define the filter product. This is a dependent version of
Filter.germSetoid.
Equations
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The filter product (a : α) → ε a at a filter l. This is a dependent version of
Filter.Germ.
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If f : α → β is constant w.r.t. l and g : β → γ, then g ∘ f : α → γ also is.
Given a map F : (α → β) → (γ → δ) that sends functions eventually equal at l to functions
eventually equal at lc, returns a map from Germ l β to Germ lc δ.
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Given a germ f : Germ l β and a function F : (α → β) → γ sending eventually equal functions
to the same value, returns the value F takes on functions having germ f at l.
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Alias of the reverse direction of Filter.Germ.coe_eq.
Alias of the reverse direction of Filter.Germ.coe_tendsto.
Given two germs f : Germ l β, and g : Germ lc α, where l : Filter α, if g tends to l,
then the composition f ∘ g is well-defined as a germ at lc.
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Given a germ f : Germ l β and a function g : γ → α, where l : Filter α, if g tends
to l along lc : Filter γ, then the composition f ∘ g is well-defined as a germ at lc.
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If a germ f : Germ l β is constant, where l : Filter α,
and a function g : γ → α tends to l along lc : Filter γ,
the germ of the composition f ∘ g is also constant.