111 lines
3.4 KiB
Text
111 lines
3.4 KiB
Text
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import homotopy.join homotopy.smash
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open eq equiv trunc function bool join sphere sphere_index sphere.ops prod
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open pointed sigma smash
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namespace spherical_fibrations
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/- classifying type of spherical fibrations -/
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definition BG (n : ℕ) : Type₁ :=
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Σ(X : Type₀), ∥ X ≃ S n..-1 ∥
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definition pointed_BG [instance] [constructor] (n : ℕ) : pointed (BG n) :=
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pointed.mk ⟨ S n..-1 , tr erfl ⟩
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definition pBG [constructor] (n : ℕ) : Type* := pointed.mk' (BG n)
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definition BG_succ (n : ℕ) : BG n → BG (n+1) :=
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begin
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intro X, cases X with X p,
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apply sigma.mk (susp X), induction p with f, apply tr,
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apply susp.equiv f
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end
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/- classifying type of pointed spherical fibrations -/
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definition BF (n : ℕ) : Type₁ :=
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Σ(X : Type*), ∥ X ≃* S. n ∥
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definition pointed_BF [instance] [constructor] (n : ℕ) : pointed (BF n) :=
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pointed.mk ⟨ S. n , tr pequiv.rfl ⟩
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definition pBF [constructor] (n : ℕ) : Type* := pointed.mk' (BF n)
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definition BF_succ (n : ℕ) : BF n → BF (n+1) :=
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begin
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intro X, cases X with X p,
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apply sigma.mk (psusp X), induction p with f, apply tr,
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apply susp.psusp_equiv f
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end
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definition BF_of_BG {n : ℕ} : BG n → BF n :=
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begin
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intro X, cases X with X p,
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apply sigma.mk (pointed.MK (susp X) susp.north),
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induction p with f, apply tr,
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apply pequiv_of_equiv (susp.equiv f),
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reflexivity
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end
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definition BG_of_BF {n : ℕ} : BF n → BG (n + 1) :=
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begin
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intro X, cases X with X hX,
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apply sigma.mk (carrier X), induction hX with fX,
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apply tr, exact fX
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end
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definition BG_mul {n m : ℕ} (X : BG n) (Y : BG m) : BG (n + m) :=
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begin
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cases X with X pX, cases Y with Y pY,
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apply sigma.mk (join X Y),
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induction pX with fX, induction pY with fY,
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apply tr, rewrite add_sub_one,
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exact (join.equiv_closed fX fY) ⬝e (join.spheres n..-1 m..-1)
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end
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definition BF_mul {n m : ℕ} (X : BF n) (Y : BF m) : BF (n + m) :=
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begin
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cases X with X hX, cases Y with Y hY,
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apply sigma.mk (psmash X Y),
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induction hX with fX, induction hY with fY, apply tr,
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exact sorry -- needs smash.spheres : psmash (S. n) (S. m) ≃ S. (n + m)
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end
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definition BF_of_BG_mul (n m : ℕ) (X : BG n) (Y : BG m)
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: BF_of_BG (BG_mul X Y) = BF_mul (BF_of_BG X) (BF_of_BG Y) :=
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sorry
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-- Thom spaces
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namespace thom
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variables {X : Type} {n : ℕ} (α : X → BF n)
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-- the canonical section of an F-object
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protected definition sec (x : X) : carrier (sigma.pr1 (α x)) :=
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Point _
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open pushout sigma
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definition thom_space : Type :=
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pushout (λx : X, ⟨x , thom.sec α x⟩) (const X unit.star)
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end thom
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/-
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Things to do:
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- Orientability and orientations
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* Thom class u ∈ ~Hⁿ(Tξ)
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* eventually prove Thom-Isomorphism (Rudyak IV.5.7)
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- define BG∞ and BF∞ as colimits of BG n and BF n
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- Ω(BF n) = ΩⁿSⁿ₁ + ΩⁿSⁿ₋₁ (self-maps of degree ±1)
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- succ_BF n is (n - 2) connected (from Freudenthal)
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- pfiber (BG_of_BF n) ≃ S. n
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- π₁(BF n)=π₁(BG n)=ℤ/2ℤ
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- double covers BSG and BSF
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- O : BF n → BG 1 = Σ(A : Type), ∥ A = bool ∥
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- BSG n = sigma O
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- π₁(BSG n)=π₁(BSF n)=O
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- BSO(n), BSTop(n)
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- find BF' n : Type₀ with BF' n ≃ BF n etc.
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- canonical bundle γₙ : ℝP(n) → ℝP∞=BO(1) → Type₀
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prove T(γₙ) = ℝP(n+1)
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-/
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end spherical_fibrations
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