Peripheral actions on free pro-p groups

The declarations the status of Tau Ceti's roadmap names, and the other results named in the modules where only this status names declarations, or in folders below the areas where only it names 2 or more, as Tau Ceti has them at commit ace60277.

TheoremThe peripheral product identity#

For every unit u ∈ ℤ_pˣ, the basis x = basis e of a free pro-p group admits conjugators c on the basis, with c 0 = 1 in positive rank, and d on the cusp such that (∏_i (c i)⁻¹ * x i ^ u * c i) * (d⁻¹ * cusp x ^ u * d) = 1, the product taken in order and ^ u the p-adic power.

TauCeti.Peripheral.exists_defect_eq_one.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1}
  [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r))
  (u : ℤ_[p]ˣ) :
  ∃ c d,
    (∀ (h0 : 0 < r), c ⟨0, h0⟩ = 1) ∧
      TauCeti.Peripheral.defect hF (TauCeti.Peripheral.basis e) (↑u) c d = 1
Uses 2 · Used by 1

TheoremSolutions at every level#

For a unit u, every peripheral level of the basis x = basis e of a free pro-p group contains a pair of conjugators whose conjugator at the first basis element is trivial when the rank is positive.

TauCeti.Peripheral.exists_mem_level.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1} [Group F]
  [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F] [TotallyDisconnectedSpace F]
  (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r)) (u : ℤ_[p]ˣ) (n : ℕ) :
  ∃ c d,
    (∀ (h0 : 0 < r), c ⟨0, h0⟩ = 1) ∧
      (c, d) ∈ TauCeti.Peripheral.level hF (TauCeti.Peripheral.basis e) (↑u) n
Uses 2 · Used by 1

TheoremThe compactness step#

If every peripheral level of a family x in a pro-p group contains a pair of conjugators whose conjugator at the first basis element is trivial when the rank is positive, then some such pair has trivial defect. The exponent u need not be a unit.

TauCeti.Peripheral.exists_defect_eq_one_of_forall_exists_mem_level.{u_1} {p r : ℕ}
  [Fact (Nat.Prime p)] {F : Type u_1} [Group F] [TopologicalSpace F] [IsTopologicalGroup F]
  [CompactSpace F] [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (x : Fin r → F)
  (u : ℤ_[p])
  (h :
    ∀ (n : ℕ),
      ∃ c d, (∀ (h0 : 0 < r), c ⟨0, h0⟩ = 1) ∧ (c, d) ∈ TauCeti.Peripheral.level hF x u n) :
  ∃ c d, (∀ (h0 : 0 < r), c ⟨0, h0⟩ = 1) ∧ TauCeti.Peripheral.defect hF x u c d = 1
Uses 2 · Used by 1

TheoremTauCeti.Peripheral.not_exists_peripheral_identity_two#

At exponent 2, no normalized peripheral product in a rank-two free pro-2 group is trivial even modulo the second closed lower-central-series term.

TauCeti.Peripheral.not_exists_peripheral_identity_two.{u_1} {F : Type u_1} [Group F]
  [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F] [TotallyDisconnectedSpace F]
  (hF : TauCeti.IsProP 2 F) (e : F ≃ₜ* TauCeti.freeProP 2 (Fin 2)) :
  ¬∃ c d,
      hF.padicPow (TauCeti.Peripheral.basis e 0) 2 *
            (c⁻¹ * hF.padicPow (TauCeti.Peripheral.basis e 1) 2 * c) *
          (d⁻¹ * hF.padicPow (TauCeti.Peripheral.cusp (TauCeti.Peripheral.basis e)) 2 * d) ∈
        TauCeti.closedLowerCentralSeries F 2
Uses 1

TheoremThe peripheral-power theorem#

For every unit u ∈ ℤ_pˣ there are a continuous automorphism φ of F, conjugators c on the basis x = basis e, with c 0 = 1 in positive rank, and a conjugator d on the cusp, such that φ (x i) = (c i)⁻¹ * x i ^ u * c i for every i and φ (cusp x) = d⁻¹ * cusp x ^ u * d, where ^ u is the p-adic power.

TauCeti.Peripheral.exists_peripheralAut.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1}
  [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r))
  (u : ℤ_[p]ˣ) :
  ∃ φ c d,
    (∀ (h0 : 0 < r), c ⟨0, h0⟩ = 1) ∧
      (∀ (i : Fin r),
          φ (TauCeti.Peripheral.basis e i) =
            (c i)⁻¹ * hF.padicPow (TauCeti.Peripheral.basis e i) ↑u * c i) ∧
        φ (TauCeti.Peripheral.cusp (TauCeti.Peripheral.basis e)) =
          d⁻¹ * hF.padicPow (TauCeti.Peripheral.cusp (TauCeti.Peripheral.basis e)) ↑u * d
Uses 2 · Used by 2

TheoremThe peripheral conjugators are not all equal#

For a free pro-p group of rank at least two and u ∈ ℤ_p other than 0 and 1, if an endomorphism φ satisfies φ (x i) = (c i)⁻¹ * x i ^ u * c i for every basis element and φ z = d⁻¹ * z ^ u * d on the cusp, then some c i differs from d.

TauCeti.Peripheral.exists_ne_of_apply_eq_conj.{u_1, u_2} {p : ℕ} [Fact (Nat.Prime p)] {F : Type u_1}
  [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] {M : Type u_2} [FunLike M F F] [MonoidHomClass M F F] {n : ℕ}
  (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin (n + 2))) {u : ℤ_[p]} (hu₀ : u ≠ 0)
  (hu₁ : u ≠ 1) (φ : M) {c : Fin (n + 2) → F} {d : F}
  (hc :
    ∀ (i : Fin (n + 2)),
      φ (TauCeti.Peripheral.basis e i) =
        (c i)⁻¹ * hF.padicPow (TauCeti.Peripheral.basis e i) u * c i)
  (hd :
    φ (TauCeti.Peripheral.cusp (TauCeti.Peripheral.basis e)) =
      d⁻¹ * hF.padicPow (TauCeti.Peripheral.cusp (TauCeti.Peripheral.basis e)) u * d) :
  ∃ i, c i ≠ d

TheoremThe permutation and the exponent are determined in rank at least two#

For the basis of a free pro-p group of rank r ≥ 2, an automorphism peripheral for (σ, u) and for (σ', u') has σ = σ' and u = u'.

TauCeti.Peripheral.IsPeripheralPermAut.unique.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1}
  [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] {hF : TauCeti.IsProP p F} {e : F ≃ₜ* TauCeti.freeProP p (Fin r)}
  (hr : 2 ≤ r) {σ σ' : Equiv.Perm (Fin (r + 1))} {u u' : ℤ_[p]ˣ} {φ : TauCeti.ContinuousAut F}
  (h : TauCeti.Peripheral.IsPeripheralPermAut hF (TauCeti.Peripheral.basis e) σ u φ)
  (h' : TauCeti.Peripheral.IsPeripheralPermAut hF (TauCeti.Peripheral.basis e) σ' u' φ) :
  σ = σ' ∧ u = u'
Used by 1

DefinitionThe permutation and the exponent of a permutation-peripheral automorphism#

The permutation and the exponent of a permutation-peripheral automorphism, for the basis of a free pro-p group of rank at least two, as a homomorphism.

TauCeti.Peripheral.permData.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1} [Group F]
  [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F] [TotallyDisconnectedSpace F]
  (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r)) (hr : 2 ≤ r) :
  ↥(TauCeti.Peripheral.peripheralPermAut hF (TauCeti.Peripheral.basis e)) →*
    Equiv.Perm (Fin (r + 1)) × ℤ_[p]ˣ
Uses 1

TheoremThe data are not determined in rank one#

In rank one the peripheral tuple is (x, x⁻¹), and an automorphism with x ↦ x ^ u is peripheral both for the trivial permutation with exponent u and for the transposition with exponent -u.

TauCeti.Peripheral.exists_isPeripheralPermAut_swap_rank_one.{u_1} {p : ℕ} [Fact (Nat.Prime p)]
  {F : Type u_1} [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin 1))
  (u : ℤ_[p]ˣ) :
  ∃ φ,
    TauCeti.Peripheral.IsPeripheralPermAut hF (TauCeti.Peripheral.basis e) 1 u φ ∧
      TauCeti.Peripheral.IsPeripheralPermAut hF (TauCeti.Peripheral.basis e) (Equiv.swap 0 1) (-u) φ
Uses 1

TheoremThe section of the exponent over the principal units#

Let F be a marked free pro-p group of positive rank, and let k ≥ 1, with k ≥ 2 when p = 2. Then the exponent character of the peripheral automorphism group has a continuous homomorphic section over the principal units U^(k) = 1 + p ^ k ℤ_p: a continuous homomorphism s : U^(k) →ₜ* peripheralAut hF (basis e) with exponent (s v) = v for every v.

TauCeti.Peripheral.exists_section_principalUnits.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1}
  [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r))
  (hr : 0 < r) {k : ℕ} (hk : 0 < k) (hk₂ : p = 2 → 2 ≤ k) :
  ∃ s, ∀ (v : ↥(TauCeti.unitsPrincipal p k)), (TauCeti.Peripheral.exponent hF e hr) (s v) = ↑v
Uses 10

TheoremThe peripheral automorphisms form a closed subgroup#

The peripheral automorphisms form a closed subgroup of ContinuousAut F for the congruence topology, when F is topologically finitely generated.

TauCeti.Peripheral.isClosed_peripheralAut.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1}
  [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (x : Fin r → F)
  (hfg : TauCeti.IsTopologicallyFinitelyGenerated F) :
  IsClosed ↑(TauCeti.Peripheral.peripheralAut hF x)
Uses 1 · Used by 1

TheoremThe exponent character is continuous#

Its graph is closed, being the peripheral graph of the basis, and its target ℤ_[p]ˣ is compact.

TauCeti.Peripheral.continuous_exponent.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1} [Group F]
  [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F] [TotallyDisconnectedSpace F]
  (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r)) (hr : 0 < r) :
  Continuous ⇑(TauCeti.Peripheral.exponent hF e hr)
Uses 2 · Used by 1

DefinitionTauCeti.Peripheral.peripheralAut#

The continuous automorphisms peripheral for x with some common unit exponent.

TauCeti.Peripheral.peripheralAut.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1} [Group F]
  [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F] [TotallyDisconnectedSpace F]
  (hF : TauCeti.IsProP p F) (x : Fin r → F) : Subgroup (TauCeti.ContinuousAut F)
Used by 5

DefinitionTauCeti.Peripheral.exponent#

The unique common unit exponent of a peripheral automorphism of a marked free pro-p group of positive rank.

TauCeti.Peripheral.exponent.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1} [Group F]
  [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F] [TotallyDisconnectedSpace F]
  (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r)) (hr : 0 < r) :
  ↥(TauCeti.Peripheral.peripheralAut hF (TauCeti.Peripheral.basis e)) →* ℤ_[p]ˣ
Uses 1 · Used by 2

TheoremTauCeti.Peripheral.peripheralAut_eq_top_rank_one#

In rank one the peripheral automorphism group is the whole group of continuous automorphisms.

TauCeti.Peripheral.peripheralAut_eq_top_rank_one.{u_1} {p : ℕ} {F : Type u_1} [Group F]
  [TopologicalSpace F] [Fact (Nat.Prime p)] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin 1)) :
  TauCeti.Peripheral.peripheralAut hF (TauCeti.Peripheral.basis e) = ⊤
Uses 2

DefinitionTauCeti.Peripheral.level#

The n-th peripheral level is the set of conjugators whose defect lies in the n-th term of the closed lower central series.

TauCeti.Peripheral.level.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1} [Group F]
  [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F] [TotallyDisconnectedSpace F]
  (hF : TauCeti.IsProP p F) (x : Fin r → F) (u : ℤ_[p]) (n : ℕ) : Set ((Fin r → F) × F)
Used by 5

TheoremTauCeti.Peripheral.exists_mem_level_succ#

A pair of conjugators whose defect lies in γ_n, for positive n, can be corrected so that its defect lies in γ_{n+1}. The corrections lie in γ_{n-1}, and the correction at the first basis element is trivial. The unit hypothesis on u is used to rescale the required graded correction.

TauCeti.Peripheral.exists_mem_level_succ.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1}
  [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r))
  (u : ℤ_[p]ˣ) (n : ℕ) (hn : 1 ≤ n) (c : Fin r → F) (d : F)
  (h : (c, d) ∈ TauCeti.Peripheral.level hF (TauCeti.Peripheral.basis e) (↑u) n) :
  ∃ c' d',
    (∀ (i : Fin r), c' i ∈ TauCeti.closedLowerCentralSeries F (n - 1)) ∧
      d' ∈ TauCeti.closedLowerCentralSeries F (n - 1) ∧
        (∀ (h0 : 0 < r), c' ⟨0, h0⟩ = 1) ∧
          (fun i => c i * c' i, d * d') ∈
            TauCeti.Peripheral.level hF (TauCeti.Peripheral.basis e) (↑u) (n + 1)
Uses 1 · Used by 1

TheoremTauCeti.Peripheral.forall_mem_level_iff#

A pair of conjugators lies in every peripheral level exactly when its defect is trivial: in a pro-p group the terms of the closed lower central series have trivial intersection.

TauCeti.Peripheral.forall_mem_level_iff.{u_1} {p r : ℕ} [Fact (Nat.Prime p)] {F : Type u_1}
  [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (x : Fin r → F) (u : ℤ_[p])
  (cd : (Fin r → F) × F) :
  (∀ (n : ℕ), cd ∈ TauCeti.Peripheral.level hF x u n) ↔
    TauCeti.Peripheral.defect hF x u cd.1 cd.2 = 1
Uses 1 · Used by 1

DefinitionThe principal units are a copy of ℤ_p#

For f ≥ 1, with f ≥ 2 when p = 2, and a unit w of exact level f, the p-adic power map l ↦ w ^ l is a topological group isomorphism from the additive group of ℤ_[p] onto U^(f) = 1 + p ^ f ℤ_p. It is onto because w topologically generates U^(f), and injective because w has infinite order.

TauCeti.principalUnitsEquiv {p : ℕ} [Fact (Nat.Prime p)] {f : ℕ} (hf : 0 < f) (hf₂ : p = 2 → 2 ≤ f)
  {w : ℤ_[p]ˣ} (hw : w ∈ TauCeti.unitsPrincipal p f) (hw' : w ∉ TauCeti.unitsPrincipal p (f + 1)) :
  Multiplicative ℤ_[p] ≃ₜ* ↥(TauCeti.unitsPrincipal p f)
Used by 1

TheoremThe peripheral-power theorem for the conjugates of the cusp#

For every unit u ∈ ℤ_pˣ there are a continuous automorphism φ of F, conjugators c on the basis x = basis e, with c 0 = 1 in positive rank, and d : F, such that φ (x i) = (c i)⁻¹ * x i ^ u * c i for every i and, for every q : F, φ carries the conjugate y = q * cusp x * q⁻¹ of the cusp to d'⁻¹ * y ^ u * d' with d' = q * d * (φ q)⁻¹. At q = 1 the conjugator is d.

TauCeti.Peripheral.exists_peripheralAut_conj_cusp.{u_1} {p r : ℕ} [Fact (Nat.Prime p)]
  {F : Type u_1} [Group F] [TopologicalSpace F] [IsTopologicalGroup F] [CompactSpace F]
  [TotallyDisconnectedSpace F] (hF : TauCeti.IsProP p F) (e : F ≃ₜ* TauCeti.freeProP p (Fin r))
  (u : ℤ_[p]ˣ) :
  ∃ φ c d,
    (∀ (h0 : 0 < r), c ⟨0, h0⟩ = 1) ∧
      (∀ (i : Fin r),
          φ (TauCeti.Peripheral.basis e i) =
            (c i)⁻¹ * hF.padicPow (TauCeti.Peripheral.basis e i) ↑u * c i) ∧
        ∀ (q : F),
          φ (q * TauCeti.Peripheral.cusp (TauCeti.Peripheral.basis e) * q⁻¹) =
            (q * d * (φ q)⁻¹)⁻¹ *
                hF.padicPow (q * TauCeti.Peripheral.cusp (TauCeti.Peripheral.basis e) * q⁻¹) ↑u *
              (q * d * (φ q)⁻¹)
Uses 1

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