Theorem: HNNExtension.induction_on
File: Mathlib/GroupTheory/HNNExtension.lean

Proof steps:
state_before: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
⊢ motive x
state_after: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
⊢ motive x
tactic: let S : Subgroup (HNNExtension G A B φ) :=
    { carrier := setOf motive
      one_mem' := by simpa using of 1
      mul_mem' := mul _ _
      inv_mem' := inv _ }
state_before: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
⊢ motive x
state_after: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
f : HNNExtension G A B φ →* ↥S := lift (HNNExtension.of.codRestrict S of) ⟨HNNExtension.t, t⟩ ⋯
⊢ motive x
tactic: let f : HNNExtension G A B φ →* S :=
    lift (HNNExtension.of.codRestrict S of)
      ⟨HNNExtension.t, t⟩ (by intro a; ext; simp [equiv_eq_conj, mul_assoc])
state_before: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
f : HNNExtension G A B φ →* ↥S := lift (HNNExtension.of.codRestrict S of) ⟨HNNExtension.t, t⟩ ⋯
⊢ motive x
state_after: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
f : HNNExtension G A B φ →* ↥S := lift (HNNExtension.of.codRestrict S of) ⟨HNNExtension.t, t⟩ ⋯
hf : S.subtype.comp f = MonoidHom.id (HNNExtension G A B φ)
⊢ motive x
tactic: have hf : S.subtype.comp f = MonoidHom.id _ :=
    hom_ext (by ext; simp [f]) (by simp [f])
state_before: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
f : HNNExtension G A B φ →* ↥S := lift (HNNExtension.of.codRestrict S of) ⟨HNNExtension.t, t⟩ ⋯
hf : S.subtype.comp f = MonoidHom.id (HNNExtension G A B φ)
⊢ motive x
state_after: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
f : HNNExtension G A B φ →* ↥S := lift (HNNExtension.of.codRestrict S of) ⟨HNNExtension.t, t⟩ ⋯
hf : S.subtype.comp f = MonoidHom.id (HNNExtension G A B φ)
⊢ motive ((MonoidHom.id (HNNExtension G A B φ)) x)
tactic: show motive (MonoidHom.id _ x)
state_before: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
f : HNNExtension G A B φ →* ↥S := lift (HNNExtension.of.codRestrict S of) ⟨HNNExtension.t, t⟩ ⋯
hf : S.subtype.comp f = MonoidHom.id (HNNExtension G A B φ)
⊢ motive ((MonoidHom.id (HNNExtension G A B φ)) x)
state_after: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
f : HNNExtension G A B φ →* ↥S := lift (HNNExtension.of.codRestrict S of) ⟨HNNExtension.t, t⟩ ⋯
hf : S.subtype.comp f = MonoidHom.id (HNNExtension G A B φ)
⊢ motive ((S.subtype.comp f) x)
tactic: rw [← hf]
state_before: G : Type u_1
inst✝² : Group G
A B : Subgroup G
φ : ↥A ≃* ↥B
H : Type u_2
inst✝¹ : Group H
M : Type u_3
inst✝ : Monoid M
motive : HNNExtension G A B φ → Prop
x : HNNExtension G A B φ
of : ∀ (g : G), motive (HNNExtension.of g)
t : motive HNNExtension.t
mul : ∀ (x y : HNNExtension G A B φ), motive x → motive y → motive (x * y)
inv : ∀ (x : HNNExtension G A B φ), motive x → motive x⁻¹
S : Subgroup (HNNExtension G A B φ) := { carrier := setOf motive, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
f : HNNExtension G A B φ →* ↥S := lift (HNNExtension.of.codRestrict S of) ⟨HNNExtension.t, t⟩ ⋯
hf : S.subtype.comp f = MonoidHom.id (HNNExtension G A B φ)
⊢ motive ((S.subtype.comp f) x)
state_after: no goals
tactic: exact (f x).2