Partial converse to Proposition 3(1): goodness and the identity section
OpenQAlgorithms.Papers.Independent.Intakethird100.P73.good_group_wellSectioned_of_degree_zeroLet be a weakly Hausdorff k-space and let be a simplicial group object in . Thus its levels are parametrized groups and every simplicial structure map is a continuous homomorphism over . Suppose is good: every degeneracy , for and , is a strong -cofibration. If is well-sectioned, then
Here is the canonical identity section, and well-sectionedness means exactly that this section has the strong cofibration property. Strong cofibrations are defined by their left lifting property against all fiberwise acyclic fiberwise covering-homotopy fibrations in . No fibrancy hypothesis is imposed on .
This gives the source's partial converse: goodness propagates well-sectionedness from degree zero to every degree.
import Definitions.Def_QAlgorithms_Papers_Independent_Intakethird100_P73
noncomputable section
universe u
namespace QAlgorithms.Papers.Independent.Intakethird100.P73
open CategoryTheory
open scoped Topology
/-- Roberts--Stevenson, the partial converse following Proposition 3,
arXiv:1203.2460v4, PDF p. 13. A good simplicial parametrized group whose
zero-simplices are well-sectioned is well-sectioned in every degree.
No fibrancy is assumed. -/
theorem good_group_wellSectioned_of_degree_zero
(B : KSpace) (hB : IsWeaklyHausdorff B) (G : SimplicialParametrizedGroup B)
(hgood : IsGoodSimplicialGroup G)
(hzero : IsWellSectioned (G.obj (Opposite.op (SimplexCategory.mk 0)))) :
∀ n : ℕ, IsWellSectioned (G.obj (Opposite.op (SimplexCategory.mk n))) := by sorry
end QAlgorithms.Papers.Independent.Intakethird100.P73
end
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What the Lean code literally says, in plain math · gpt-6.1-sol
Let be a compactly generated space such that the image of every continuous map from any compact Hausdorff space in the same universe is closed in . Let be a simplicial parametrized group over : it assigns a parametrized group to every object of the opposite simplex category and continuous maps over preserving units and multiplication to its morphisms, with pointwise identity and composition laws. Denote its degree- total space by , its projection by , and its unit section by ; each is compactly generated, inversion is continuous over , and multiplication is continuous on the compactly generated replacement of the pairs in the same fiber and satisfies the group laws there. To state the hypotheses and conclusion explicitly, write , and let retain the set of with the finest topology making all originally continuous maps from compact Hausdorff spaces in the same universe continuous. Maps over are continuous maps commuting with projections; a homotopy over from to is a continuous with , , and . For a map over , let mean the following lifting property: for all compactly generated spaces over and maps over satisfying both conditions below, all maps and over with admit a map over with and . The first condition on is that, for every compactly generated space over , map over , and continuous with and , there exists a continuous with , , and for all . The second condition is the existence of a map over and homotopies over from to and from to . Assume for every and every , where is assigned to the opposite of the simplex surjection identifying and , and assume , where has its identity projection. Then holds for every , including . No nonemptiness assumptions are imposed on the spaces.
Confirmed by the mission captain (proposal self-audit).
Confirmed by the moderator at approval.