Module

Core.lean

Nyll.ValuedFieldTheory.Ramification.LocalField.Core
23 declarations indexed from sourceView source ↗

Upper ramification jumps

The actual finite-level upper filtration attached to the canonical complete-DVF structure of a nonarchimedean local field, together with its right-limit subgroup and the intrinsic predicate for an upper jump.

Imports7
Imported by13

Declarations

LocalFieldTheory.chosenLocalExtensionCompleteDVF_hasUniqueDVFValuationExtension

Uniqueness after forgetting completeness, in the form consumed by the real lower and upper ramification APIs.

Source context 6 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace LocalFieldTheory
theorem chosenLocalExtensionCompleteDVF_hasUniqueDVFValuationExtension
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [Algebra.IsSeparable K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K] :
    RamificationTheory.DiscreteValuationField.DVF.HasUniqueValuationExtension.{0, 0, 0, 0, y}
      (localCompleteDVF K).toDVF
      (chosenLocalExtensionCompleteDVF K L).toDVF
RamificationTheory.LocalField.completeDVFComapAlgEquiv

Pull a complete discrete valuation back along a field equivalence.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
def completeDVFComapAlgEquiv
    {L M : Type} [Field L] [Field M]
    (target : CompleteDVF.{0, 0} M) (e : L ≃+* M) :
    CompleteDVF.{0, 0} L where
  ValueGroup := target.ValueGroup
  valuation := target.valuation.comap e.toRingHom
  instCompleteDiscrete :=
    Valuation.isCompleteDiscrete_comap_ringEquiv target.valuation e
RamificationTheory.LocalField.completeDVFComapAlgEquiv_hasExtension

Pullback along a base-linear equivalence preserves extension of the base valuation.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem completeDVFComapAlgEquiv_hasExtension
    (K L M : Type) [Field K] [Field L] [Field M]
    [Algebra K L] [Algebra K M]
    (base : CompleteDVF.{0, 0} K)
    (target : CompleteDVF.{0, 0} M)
    [base.valuation.HasExtension target.valuation]
    (e : L ≃ₐ[K] M) :
    base.valuation.HasExtension
      (completeDVFComapAlgEquiv target e.toRingEquiv).valuation where
  val_isEquiv_comap := by
    rw [_root_.Valuation.isEquiv_iff_val_le_one]
    intro a
    change
      base.valuation a ≤ 1 ↔
        target.valuation (e ((algebraMap K L) a)) ≤ 1
    rw [e.commutes]
    exact
      (_root_.Valuation.HasExtension.val_map_le_one_iff
        (vR := base.valuation) (vA := target.valuation) a).symm
RamificationTheory.LocalField.localLowerRamificationGroup

The actual real lower ramification group of an arbitrary finite Galois extension of nonarchimedean local fields, using its integral-closure valuation.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
def localLowerRamificationGroup
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) : Subgroup Gal(L / K)
RamificationTheory.LocalField.localUpperRamificationGroup

The actual real upper ramification group of an arbitrary finite Galois extension of nonarchimedean local fields.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
def localUpperRamificationGroup
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) : Subgroup Gal(L / K)
RamificationTheory.LocalField.localUpperRamificationGroup_map_autCongr

A base-linear field equivalence transports every local upper ramification group to the corresponding group of the equivalent extension.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localUpperRamificationGroup_map_autCongr
    (K L M : Type)
    [Field K] [Field L] [Field M]
    [Algebra K L] [Algebra K M]
    [FiniteDimensional K L] [FiniteDimensional K M]
    [IsGalois K L] [IsGalois K M]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (e : L ≃ₐ[K] M) (t : ℝ) :
    Subgroup.map (AlgEquiv.autCongr e).toMonoidHom
        (localUpperRamificationGroup K L t) =
      localUpperRamificationGroup K M t
RamificationTheory.LocalField.fixedFieldUpperRamificationGroup_map_autCongr
Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem fixedFieldUpperRamificationGroup_map_autCongr
    (K L M : Type)
    [Field K] [Field L] [Field M]
    [Algebra K L] [Algebra K M]
    [FiniteDimensional K L] [FiniteDimensional K M]
    [IsGalois K L] [IsGalois K M]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (H : Subgroup Gal(L/K)) [H.Normal]
    (e : IntermediateField.fixedField H ≃ₐ[K] M)
    (t : ℝ) :
    Subgroup.map (AlgEquiv.autCongr e).toMonoidHom
        (fixedFieldUpperRamificationGroup
          (chosenLocalExtensionCompleteDVF_hasUniqueDVFValuationExtension
            K L) H t) =
      localUpperRamificationGroup K M t
RamificationTheory.LocalField.fixedFieldUpperRamificationGroup_eq_local
Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem fixedFieldUpperRamificationGroup_eq_local
    (K L : Type)
    [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (H : Subgroup Gal(L/K)) [H.Normal]
    (t : ℝ) :
    fixedFieldUpperRamificationGroup
        (chosenLocalExtensionCompleteDVF_hasUniqueDVFValuationExtension
          K L) H t =
      localUpperRamificationGroup K (IntermediateField.fixedField H) t
RamificationTheory.LocalField.localUpperRamificationGroup_map_restrict

Upper ramification groups descend along restriction between finite Galois intermediate fields in a common separable closure.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localUpperRamificationGroup_map_restrict
    (K : Type) [Field K]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (E F : IntermediateField K (SeparableClosure K)) (hEF : E ≤ F)
    [FiniteDimensional K E] [FiniteDimensional K F]
    [IsGalois K E] [IsGalois K F]
    (t : ℝ) :
    Subgroup.map
        (intermediateFieldRestrictNormalHom E F hEF)
        (localUpperRamificationGroup K F t) =
      localUpperRamificationGroup K E t
RamificationTheory.LocalField.localUpperRamificationGroup_antitone

The local upper ramification filtration is antitone.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localUpperRamificationGroup_antitone
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K] :
    Antitone (localUpperRamificationGroup K L)
RamificationTheory.LocalField.localUpperRamificationGroupAfter

The subgroup immediately after an upper ramification index for an arbitrary finite local Galois extension.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
def localUpperRamificationGroupAfter
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) : Subgroup Gal(L / K)
RamificationTheory.LocalField.localUpperRamificationGroupAfter_le

The right-limit upper group lies in the group at the limiting index.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localUpperRamificationGroupAfter_le
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) :
    localUpperRamificationGroupAfter K L t ≤
      localUpperRamificationGroup K L t
RamificationTheory.LocalField.IsLocalUpperRamificationJump

Intrinsic upper-jump predicate for an arbitrary finite local Galois extension.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
def IsLocalUpperRamificationJump
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) : Prop
RamificationTheory.LocalField.localUpperRamificationGroupAfter_map_restrict

Restriction along a finite Galois tower carries the right-limit of the upper filtration onto the corresponding right-limit downstairs.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localUpperRamificationGroupAfter_map_restrict
    (K : Type) [Field K]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (E F : IntermediateField K (SeparableClosure K)) (hEF : E ≤ F)
    [FiniteDimensional K E] [FiniteDimensional K F]
    [IsGalois K E] [IsGalois K F]
    (t : ℝ) :
    Subgroup.map
        (intermediateFieldRestrictNormalHom E F hEF)
        (localUpperRamificationGroupAfter K F t) =
      localUpperRamificationGroupAfter K E t
RamificationTheory.LocalField.isLocalUpperRamificationJump_of_map_restrict

Every upper jump downstairs in a finite Galois tower was already an upper jump upstairs. Thus quotienting an extension cannot create new break indices.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem isLocalUpperRamificationJump_of_map_restrict
    (K : Type) [Field K]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (E F : IntermediateField K (SeparableClosure K)) (hEF : E ≤ F)
    [FiniteDimensional K E] [FiniteDimensional K F]
    [IsGalois K E] [IsGalois K F]
    {t : ℝ} (ht : IsLocalUpperRamificationJump K E t) :
    IsLocalUpperRamificationJump K F t
RamificationTheory.LocalField.localInverseHerbrandFunction_eq_self_of_nonpos
Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localInverseHerbrandFunction_eq_self_of_nonpos
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) (ht : t ≤ 0) :
    inverseHerbrandFunctionOfUniqueExtension
        (base := (localCompleteDVF K).toDVF)
        (target := (chosenLocalExtensionCompleteDVF K L).toDVF)
        (chosenLocalExtensionCompleteDVF_hasUniqueDVFValuationExtension K L)
        t =
      t
RamificationTheory.LocalField.localUpperRamificationGroup_eq_localLowerRamificationGroup_of_nonpos

At every nonpositive index the inverse Herbrand function is the identity, so upper and lower numbering agree.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localUpperRamificationGroup_eq_localLowerRamificationGroup_of_nonpos
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) (ht : t ≤ 0) :
    localUpperRamificationGroup K L t =
      localLowerRamificationGroup K L t
RamificationTheory.LocalField.localLowerRamificationGroup_eq_zero_of_neg_one_lt_of_nonpos

The lower filtration is constant between the distinguished endpoints -1 and 0: every such real index imposes exactly the first maximal-ideal power.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localLowerRamificationGroup_eq_zero_of_neg_one_lt_of_nonpos
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) (hneg : -1 < t) (ht : t ≤ 0) :
    localLowerRamificationGroup K L t =
      localLowerRamificationGroup K L 0
RamificationTheory.LocalField.localUpperRamificationGroup_eq_zero_of_neg_one_lt_of_nonpos

The upper filtration is constant on the half-open interval (-1, 0].

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localUpperRamificationGroup_eq_zero_of_neg_one_lt_of_nonpos
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) (hneg : -1 < t) (ht : t ≤ 0) :
    localUpperRamificationGroup K L t =
      localUpperRamificationGroup K L 0
RamificationTheory.LocalField.localUpperRamificationGroup_eq_top_of_le_neg_one

At and below -1, the local upper ramification group is the full Galois group.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem localUpperRamificationGroup_eq_top_of_le_neg_one
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) (ht : t ≤ -1) :
    localUpperRamificationGroup K L t = ⊤
RamificationTheory.LocalField.not_isLocalUpperRamificationJump_of_lt_neg_one

No upper jump occurs strictly below the distinguished endpoint -1.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem not_isLocalUpperRamificationJump_of_lt_neg_one
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) (ht : t < -1) :
    ¬ IsLocalUpperRamificationJump K L t
RamificationTheory.LocalField.not_isLocalUpperRamificationJump_of_neg_one_lt_of_lt_zero

No upper jump occurs strictly between -1 and 0.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem not_isLocalUpperRamificationJump_of_neg_one_lt_of_lt_zero
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    (t : ℝ) (hneg : -1 < t) (ht : t < 0) :
    ¬ IsLocalUpperRamificationJump K L t
RamificationTheory.LocalField.isLocalUpperRamificationJump_eq_neg_one_or_nonneg

Every local upper jump is either the possible endpoint -1 or a nonnegative index.

Source context 10 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open ValuationTheory.DiscreteValuationField
open ValuationTheory.DiscreteValuationField.ValuedExtension
open scoped ValuativeRel
universe y
namespace RamificationTheory.LocalField
open LocalFieldTheory
open RamificationTheory
open RamificationTheory.HilbertRamification
open RamificationTheory.HilbertRamification.Higher
theorem isLocalUpperRamificationJump_eq_neg_one_or_nonneg
    (K L : Type) [Field K] [Field L] [Algebra K L]
    [FiniteDimensional K L] [IsGalois K L]
    [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    {t : ℝ} (ht : IsLocalUpperRamificationJump K L t) :
    t = -1 ∨ 0 ≤ t