Tools for compatibilities between Dold-Kan equivalences
The purpose of this file is to introduce tools which will enable the
construction of the Dold-Kan equivalence SimplicialObject C ≌ ChainComplex C ℕ
for a pseudoabelian category C from the equivalence
Karoubi (SimplicialObject C) ≌ Karoubi (ChainComplex C ℕ) and the two
equivalences simplicial_object C ≅ Karoubi (SimplicialObject C) and
ChainComplex C ℕ ≅ Karoubi (ChainComplex C ℕ).
It is certainly possible to get an equivalence SimplicialObject C ≌ ChainComplex C ℕ
using a compositions of the three equivalences above, but then neither the functor
nor the inverse would have good definitional properties. For example, it would be better
if the inverse functor of the equivalence was exactly the functor
Γ₀ : SimplicialObject C ⥤ ChainComplex C ℕ which was constructed in FunctorGamma.lean.
In this file, given four categories A, A', B, B', equivalences eA : A ≅ A',
eB : B ≅ B', e' : A' ≅ B', functors F : A ⥤ B', G : B ⥤ A equipped with certain
compatibilities, we construct successive equivalences:
equivalence₀fromAtoB', which is the composition ofeAande'.equivalence₁fromAtoB', with the same inverse functor asequivalence₀, but whose functor isF.equivalence₂fromAtoB, which is the composition ofequivalence₁and the inverse ofeB:equivalencefromAtoB, which has the same functorF ⋙ eB.inverseasequivalence₂, but whose inverse functor isG.
When extra assumptions are given, we shall also provide simplification lemmas for the
unit and counit isomorphisms of equivalence.
(See Equivalence.lean for the general strategy of proof of the Dold-Kan equivalence.)
A basic equivalence A ≅ B' obtained by composing eA : A ≅ A' and e' : A' ≅ B'.
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An intermediate equivalence A ≅ B' whose functor is F and whose inverse is
e'.inverse ⋙ eA.inverse.
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The counit isomorphism of the equivalence equivalence₁ between A and B'.
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The unit isomorphism of the equivalence equivalence₁ between A and B'.
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An intermediate equivalence A ≅ B obtained as the composition of equivalence₁ and
the inverse of eB : B ≌ B'.
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The counit isomorphism of the equivalence equivalence₂ between A and B.
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The unit isomorphism of the equivalence equivalence₂ between A and B.
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The equivalence A ≅ B whose functor is F ⋙ eB.inverse and
whose inverse is G : B ≅ A.
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The isomorphism eB.functor ⋙ e'.inverse ⋙ e'.functor ≅ eB.functor deduced
from the counit isomorphism of e'.
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The isomorphism eB.functor ⋙ e'.inverse ⋙ e'.functor ≅ eB.functor deduced
from the isomorphisms hF : eA.functor ⋙ e'.functor ≅ F,
hG : eB.functor ⋙ e'.inverse ≅ G ⋙ eA.functor and the datum of
an isomorphism η : G ⋙ F ≅ eB.functor.
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The counit isomorphism of equivalence.
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The isomorphism eA.functor ≅ F ⋙ e'.inverse deduced from the
unit isomorphism of e' and the isomorphism hF : eA.functor ⋙ e'.functor ≅ F.
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The unit isomorphism of equivalence.
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