-- Mathlib/RingTheory/WittVector/Domain.lean
theorem eq_iterate_verschiebung {x : 𝕎 R} {n : ℕ} (h : ∀ i < n, x.coeff i = 0) :
    x = verschiebung^[n] (x.shift n)

Proof state:
case zero.mk'
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
coeff✝ : ℕ → R
h : ∀ i < 0, { coeff := coeff✝ }.coeff i = 0
⊢ { coeff := coeff✝ } = (⇑verschiebung)^[0] ({ coeff := coeff✝ }.shift 0)

Tactic:
simp [shift]

Result:
no goals

Proof state:
case succ
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
k : ℕ
ih : (∀ i < k, x.coeff i = 0) → x = (⇑verschiebung)^[k] (x.shift k)
h : ∀ i < k + 1, x.coeff i = 0
⊢ x = (⇑verschiebung)^[k + 1] (x.shift (k + 1))

Tactic:
dsimp

Result:
case succ
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
k : ℕ
ih : (∀ i < k, x.coeff i = 0) → x = (⇑verschiebung)^[k] (x.shift k)
h : ∀ i < k + 1, x.coeff i = 0
⊢ x = (⇑verschiebung)^[k] (verschiebung (x.shift (k + 1)))

Proof state:
case succ
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
k : ℕ
ih : (∀ i < k, x.coeff i = 0) → x = (⇑verschiebung)^[k] (x.shift k)
h : ∀ i < k + 1, x.coeff i = 0
⊢ x = (⇑verschiebung)^[k] (x.shift k)

Tactic:
exact ih fun i hi => h _ (hi.trans (Nat.lt_succ_self _))

Result:
no goals

Proof state:
case succ.h
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
k : ℕ
ih : (∀ i < k, x.coeff i = 0) → x = (⇑verschiebung)^[k] (x.shift k)
h : ∀ i < k + 1, x.coeff i = 0
⊢ ∀ i < k + 1, x.coeff i = 0

Tactic:
exact h

Result:
no goals

Proof state:
case zero
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
h : ∀ i < 0, x.coeff i = 0
⊢ x = (⇑verschiebung)^[0] (x.shift 0)

Tactic:
cases x

Result:
case zero.mk'
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
coeff✝ : ℕ → R
h : ∀ i < 0, { coeff := coeff✝ }.coeff i = 0
⊢ { coeff := coeff✝ } = (⇑verschiebung)^[0] ({ coeff := coeff✝ }.shift 0)

Proof state:
case succ
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
k : ℕ
ih : (∀ i < k, x.coeff i = 0) → x = (⇑verschiebung)^[k] (x.shift k)
h : ∀ i < k + 1, x.coeff i = 0
⊢ x = (⇑verschiebung)^[k] (verschiebung (x.shift (k + 1)))

Tactic:
rw [verschiebung_shift]

Result:
case succ
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
k : ℕ
ih : (∀ i < k, x.coeff i = 0) → x = (⇑verschiebung)^[k] (x.shift k)
h : ∀ i < k + 1, x.coeff i = 0
⊢ x = (⇑verschiebung)^[k] (x.shift k)

case succ.h
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
k : ℕ
ih : (∀ i < k, x.coeff i = 0) → x = (⇑verschiebung)^[k] (x.shift k)
h : ∀ i < k + 1, x.coeff i = 0
⊢ ∀ i < k + 1, x.coeff i = 0

Proof state:
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
n : ℕ
h : ∀ i < n, x.coeff i = 0
⊢ x = (⇑verschiebung)^[n] (x.shift n)

Tactic:
induction' n with k ih

Result:
case zero
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
h : ∀ i < 0, x.coeff i = 0
⊢ x = (⇑verschiebung)^[0] (x.shift 0)

case succ
p : ℕ
R : Type u_1
hp : Fact (Nat.Prime p)
inst✝ : CommRing R
x : 𝕎 R
k : ℕ
ih : (∀ i < k, x.coeff i = 0) → x = (⇑verschiebung)^[k] (x.shift k)
h : ∀ i < k + 1, x.coeff i = 0
⊢ x = (⇑verschiebung)^[k + 1] (x.shift (k + 1))