-- Mathlib/GroupTheory/Perm/List.lean
theorem formPerm_ext_iff {x y x' y' : α} {l l' : List α} (hd : Nodup (x :: y :: l))
    (hd' : Nodup (x' :: y' :: l')) :
    formPerm (x :: y :: l) = formPerm (x' :: y' :: l') ↔ (x :: y :: l) ~r (x' :: y' :: l')

Proof state:
case h
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
⊢ (x :: y :: l).rotate n = x' :: y' :: l'

Tactic:
apply List.ext_getElem

Result:
case h.hl
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
⊢ ((x :: y :: l).rotate n).length = (x' :: y' :: l').length

case h.h
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
⊢ ∀ (i : ℕ) (h₁ : i < ((x :: y :: l).rotate n).length) (h₂ : i < (x' :: y' :: l').length),
    ((x :: y :: l).rotate n)[i] = (x' :: y' :: l')[i]

Proof state:
case h.h.succ
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
k : ℕ
IH :
  ∀ (hk : k < ((x :: y :: l).rotate n).length) (hk' : k < (x' :: y' :: l').length),
    (x :: y :: l)[(k + n) % (x :: y :: l).length] = (x' :: y' :: l')[k]
hk : k + 1 < ((x :: y :: l).rotate n).length
hk' : k + 1 < (x' :: y' :: l').length
⊢ (x :: y :: l)[((k + 1) % (x' :: y' :: l').length + n) % (x :: y :: l).length] =
    (x :: y :: l)[((k + n) % (x :: y :: l).length + 1) % (x :: y :: l).length]

Tactic:
congr 1

Result:
case h.h.succ.e_i
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
k : ℕ
IH :
  ∀ (hk : k < ((x :: y :: l).rotate n).length) (hk' : k < (x' :: y' :: l').length),
    (x :: y :: l)[(k + n) % (x :: y :: l).length] = (x' :: y' :: l')[k]
hk : k + 1 < ((x :: y :: l).rotate n).length
hk' : k + 1 < (x' :: y' :: l').length
⊢ ((k + 1) % (x' :: y' :: l').length + n) % (x :: y :: l).length =
    ((k + n) % (x :: y :: l).length + 1) % (x :: y :: l).length

Proof state:
case h.hl
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
⊢ ((x :: y :: l).rotate n).length = (x' :: y' :: l').length

Tactic:
rw [length_rotate, hl]

Result:
no goals

Proof state:
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
⊢ x' ∈ x :: y :: l

Tactic:
have : x' ∈ { z | formPerm (x :: y :: l) z ≠ z } := by
  rw [Set.mem_setOf_eq, h x', formPerm_apply_head _ _ _ hd']
  simp only [mem_cons, nodup_cons] at hd'
  push_neg at hd'
  exact hd'.left.left.symm

Result:
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
this : x' ∈ {z | (x :: y :: l).formPerm z ≠ z}
⊢ x' ∈ x :: y :: l

Proof state:
case h.h.succ
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
k : ℕ
IH :
  ∀ (hk : k < ((x :: y :: l).rotate n).length) (hk' : k < (x' :: y' :: l').length),
    (x :: y :: l)[(k + n) % (x :: y :: l).length] = (x' :: y' :: l')[k]
hk : k + 1 < ((x :: y :: l).rotate n).length
hk' : k + 1 < (x' :: y' :: l').length
⊢ (x :: y :: l)[((k + 1) % (x' :: y' :: l').length + n) % (x :: y :: l).length] =
    (x' :: y' :: l')[(k + 1) % (x' :: y' :: l').length]

Tactic:
rw [← formPerm_apply_getElem _ hd' k (k.lt_succ_self.trans hk'),
  ← IH (k.lt_succ_self.trans hk), ← h, formPerm_apply_getElem _ hd]

Result:
case h.h.succ
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
k : ℕ
IH :
  ∀ (hk : k < ((x :: y :: l).rotate n).length) (hk' : k < (x' :: y' :: l').length),
    (x :: y :: l)[(k + n) % (x :: y :: l).length] = (x' :: y' :: l')[k]
hk : k + 1 < ((x :: y :: l).rotate n).length
hk' : k + 1 < (x' :: y' :: l').length
⊢ (x :: y :: l)[((k + 1) % (x' :: y' :: l').length + n) % (x :: y :: l).length] =
    (x :: y :: l)[((k + n) % (x :: y :: l).length + 1) % (x :: y :: l).length]

Proof state:
case h.h.zero.e_i
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
hl : (x :: y :: l).length = (x' :: y' :: l').length
hk : 0 < ((x :: y :: l).rotate n).length
hk' : 0 < (x' :: y' :: l').length
⊢ (0 + n) % (x :: y :: l).length = n

Tactic:
simpa using hn

Result:
no goals

Proof state:
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
⊢ (x :: y :: l).toFinset = (x' :: y' :: l').toFinset

Tactic:
rw [← Finset.coe_inj, ← support_formPerm_of_nodup' _ hd (by simp), ←
  support_formPerm_of_nodup' _ hd' (by simp)]

Result:
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
hx : x' ∈ x :: y :: l
n : ℕ
hn : n < (x :: y :: l).length
hx' : (x :: y :: l).get ⟨n, hn⟩ = x'
⊢ {x_1 | (x :: y :: l).formPerm x_1 ≠ x_1} = {x | (x' :: y' :: l').formPerm x ≠ x}

Proof state:
α : Type u_1
inst✝ : DecidableEq α
x y x' y' : α
l l' : List α
hd : (x :: y :: l).Nodup
hd' : (x' :: y' :: l').Nodup
h : ∀ (x_1 : α), (x :: y :: l).formPerm x_1 = (x' :: y' :: l').formPerm x_1
this : x' ∈ {z | (x :: y :: l).formPerm z ≠ z}
⊢ x' ∈ x :: y :: l

Tactic:
simpa using support_formPerm_le' _ this

Result:
no goals