-- Mathlib/RingTheory/WittVector/IsPoly.lean
theorem ext [Fact p.Prime] {f g} (hf : IsPoly p f) (hg : IsPoly p g)
    (h : ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R) (n : ℕ),
        ghostComponent n (f x) = ghostComponent n (g x)) :
    ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R), f x = g x

Proof state:
case h.e'_3
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
ψ : ℕ → MvPolynomial ℕ ℤ
hg : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (g x).coeff = fun n => (aeval x.coeff) (ψ n)
R✝ : Type u
_Rcr✝ : CommRing R✝
x✝ : 𝕎 R✝
n k : ℕ
x : ℕ → ℤ
h :
  (eval₂Hom (algebraMap ℤ (ULift.{u, 0} ℤ)) (f (mk p fun i => { down := x i })).coeff) (wittPolynomial p ℤ k) =
    (eval₂Hom (algebraMap ℤ (ULift.{u, 0} ℤ)) (g (mk p fun i => { down := x i })).coeff) (wittPolynomial p ℤ k)
⊢ (eval₂Hom ((↑ULift.ringEquiv.symm).comp ((MvPolynomial.eval x).comp C)) fun i =>
        ↑ULift.ringEquiv.symm ((MvPolynomial.eval x) (ψ i)))
      (wittPolynomial p ℤ k) =
    (eval₂Hom (algebraMap ℤ (ULift.{u, 0} ℤ)) (g (mk p fun i => { down := x i })).coeff) (wittPolynomial p ℤ k)

Tactic:
simp only [hf, hg, MvPolynomial.eval, map_eval₂Hom]

Result:
case h.e'_3
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
ψ : ℕ → MvPolynomial ℕ ℤ
hg : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (g x).coeff = fun n => (aeval x.coeff) (ψ n)
R✝ : Type u
_Rcr✝ : CommRing R✝
x✝ : 𝕎 R✝
n k : ℕ
x : ℕ → ℤ
h :
  (eval₂Hom (algebraMap ℤ (ULift.{u, 0} ℤ)) (f (mk p fun i => { down := x i })).coeff) (wittPolynomial p ℤ k) =
    (eval₂Hom (algebraMap ℤ (ULift.{u, 0} ℤ)) (g (mk p fun i => { down := x i })).coeff) (wittPolynomial p ℤ k)
⊢ (eval₂Hom ((↑ULift.ringEquiv.symm).comp ((eval₂Hom (RingHom.id ℤ) x).comp C)) fun i =>
        (eval₂Hom ((↑ULift.ringEquiv.symm).comp (RingHom.id ℤ)) fun i => ↑ULift.ringEquiv.symm (x i)) (ψ i))
      (wittPolynomial p ℤ k) =
    (eval₂Hom (algebraMap ℤ (ULift.{u, 0} ℤ)) fun n => (aeval (mk p fun i => { down := x i }).coeff) (ψ n))
      (wittPolynomial p ℤ k)

Proof state:
case mk'.intro.mk'.intro.h.h
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
h : ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R) (n : ℕ), (ghostComponent n) (f x) = (ghostComponent n) (g x)
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
ψ : ℕ → MvPolynomial ℕ ℤ
hg : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (g x).coeff = fun n => (aeval x.coeff) (ψ n)
R✝ : Type u
_Rcr✝ : CommRing R✝
x✝ : 𝕎 R✝
n k : ℕ
⊢ ∀ (x : ℕ → ℤ),
    (MvPolynomial.eval x) ((bind₁ φ) (wittPolynomial p ℤ k)) = (MvPolynomial.eval x) ((bind₁ ψ) (wittPolynomial p ℤ k))

Tactic:
intro x

Result:
case mk'.intro.mk'.intro.h.h
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
h : ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R) (n : ℕ), (ghostComponent n) (f x) = (ghostComponent n) (g x)
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
ψ : ℕ → MvPolynomial ℕ ℤ
hg : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (g x).coeff = fun n => (aeval x.coeff) (ψ n)
R✝ : Type u
_Rcr✝ : CommRing R✝
x✝ : 𝕎 R✝
n k : ℕ
x : ℕ → ℤ
⊢ (MvPolynomial.eval x) ((bind₁ φ) (wittPolynomial p ℤ k)) = (MvPolynomial.eval x) ((bind₁ ψ) (wittPolynomial p ℤ k))

Proof state:
case mk'.intro.mk'.intro.h
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
h : ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R) (n : ℕ), (ghostComponent n) (f x) = (ghostComponent n) (g x)
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
ψ : ℕ → MvPolynomial ℕ ℤ
hg : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (g x).coeff = fun n => (aeval x.coeff) (ψ n)
R✝ : Type u
_Rcr✝ : CommRing R✝
x✝ : 𝕎 R✝
n : ℕ
⊢ ∀ (n : ℕ), (bind₁ φ) (wittPolynomial p ℤ n) = (bind₁ ψ) (wittPolynomial p ℤ n)

Tactic:
intro k

Result:
case mk'.intro.mk'.intro.h
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
h : ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R) (n : ℕ), (ghostComponent n) (f x) = (ghostComponent n) (g x)
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
ψ : ℕ → MvPolynomial ℕ ℤ
hg : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (g x).coeff = fun n => (aeval x.coeff) (ψ n)
R✝ : Type u
_Rcr✝ : CommRing R✝
x✝ : 𝕎 R✝
n k : ℕ
⊢ (bind₁ φ) (wittPolynomial p ℤ k) = (bind₁ ψ) (wittPolynomial p ℤ k)

Proof state:
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
hf : IsPoly p f
hg : IsPoly p g
h : ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R) (n : ℕ), (ghostComponent n) (f x) = (ghostComponent n) (g x)
⊢ ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R), f x = g x

Tactic:
obtain ⟨φ, hf⟩ := hf

Result:
case mk'.intro
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
hg : IsPoly p g
h : ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R) (n : ℕ), (ghostComponent n) (f x) = (ghostComponent n) (g x)
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
⊢ ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R), f x = g x

Proof state:
case mk'.intro.mk'.intro.h.h
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
h : ∀ (R : Type u) [_Rcr : CommRing R] (x : 𝕎 R) (n : ℕ), (ghostComponent n) (f x) = (ghostComponent n) (g x)
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
ψ : ℕ → MvPolynomial ℕ ℤ
hg : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (g x).coeff = fun n => (aeval x.coeff) (ψ n)
R✝ : Type u
_Rcr✝ : CommRing R✝
x✝ : 𝕎 R✝
n k : ℕ
x : ℕ → ℤ
⊢ (eval₂Hom ((MvPolynomial.eval x).comp C) fun i => (MvPolynomial.eval x) (φ i)) (wittPolynomial p ℤ k) =
    (eval₂Hom ((MvPolynomial.eval x).comp C) fun i => (MvPolynomial.eval x) (ψ i)) (wittPolynomial p ℤ k)

Tactic:
specialize h (ULift ℤ) (mk p fun i => ⟨x i⟩) k

Result:
case mk'.intro.mk'.intro.h.h
p : ℕ
inst✝ : Fact (Nat.Prime p)
f g : ⦃R : Type u⦄ → [inst : CommRing R] → 𝕎 R → 𝕎 R
φ : ℕ → MvPolynomial ℕ ℤ
hf : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (f x).coeff = fun n => (aeval x.coeff) (φ n)
ψ : ℕ → MvPolynomial ℕ ℤ
hg : ∀ ⦃R : Type u⦄ [inst : CommRing R] (x : 𝕎 R), (g x).coeff = fun n => (aeval x.coeff) (ψ n)
R✝ : Type u
_Rcr✝ : CommRing R✝
x✝ : 𝕎 R✝
n k : ℕ
x : ℕ → ℤ
h : (ghostComponent k) (f (mk p fun i => { down := x i })) = (ghostComponent k) (g (mk p fun i => { down := x i }))
⊢ (eval₂Hom ((MvPolynomial.eval x).comp C) fun i => (MvPolynomial.eval x) (φ i)) (wittPolynomial p ℤ k) =
    (eval₂Hom ((MvPolynomial.eval x).comp C) fun i => (MvPolynomial.eval x) (ψ i)) (wittPolynomial p ℤ k)