instance : StarAlgEquivClass (A ≃⋆ₐ[R] B) R A B
    where
  coe f := f.toFun
  inv f := f.invFun
  left_inv f := f.left_inv
  right_inv f := f.right_inv
  coe_injective' f g h₁ h₂ := by
    rcases f with ⟨⟨⟨_, _, _⟩, _⟩, _⟩
    

Proof state:
case mk.mk.mk
F : Type u_1
R : Type u_2
A : Type u_3
B : Type u_4
C : Type u_5
inst✝¹¹ : Add A
inst✝¹⁰ : Add B
inst✝⁹ : Mul A
inst✝⁸ : Mul B
inst✝⁷ : SMul R A
inst✝⁶ : SMul R B
inst✝⁵ : Star A
inst✝⁴ : Star B
inst✝³ : Add C
inst✝² : Mul C
inst✝¹ : SMul R C
inst✝ : Star C
g : A ≃⋆ₐ[R] B
toFun✝ : A → B
invFun✝ : B → A
left_inv✝ : Function.LeftInverse invFun✝ toFun✝
right_inv✝ : Function.RightInverse invFun✝ toFun✝
map_mul'✝ :
  ∀ (x y : A),
    Equiv.toFun { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ } (x * y) =
      Equiv.toFun { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ } x *
        Equiv.toFun { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ } y
map_add'✝ :
  ∀ (x y : A),
    Equiv.toFun { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ } (x + y) =
      Equiv.toFun { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ } x +
        Equiv.toFun { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ } y
map_star'✝ :
  ∀ (a : A),
    Equiv.toFun
        { toEquiv := { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ },
            map_mul' := map_mul'✝, map_add' := map_add'✝ }.toEquiv
        (star a) =
      star
        (Equiv.toFun
          { toEquiv := { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ },
              map_mul' := map_mul'✝, map_add' := map_add'✝ }.toEquiv
          a)
map_smul'✝ :
  ∀ (r : R) (a : A),
    Equiv.toFun
        { toEquiv := { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ },
            map_mul' := map_mul'✝, map_add' := map_add'✝ }.toEquiv
        (r • a) =
      r •
        Equiv.toFun
          { toEquiv := { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ },
              map_mul' := map_mul'✝, map_add' := map_add'✝ }.toEquiv
          a
h₁ :
  (fun f => f.toFun)
      {
        toRingEquiv :=
          { toEquiv := { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ },
            map_mul' := map_mul'✝, map_add' := map_add'✝ },
        map_star' := map_star'✝, map_smul' := map_smul'✝ } =
    (fun f => f.toFun) g
h₂ :
  (fun f => f.invFun)
      {
        toRingEquiv :=
          { toEquiv := { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ },
            map_mul' := map_mul'✝, map_add' := map_add'✝ },
        map_star' := map_star'✝, map_smul' := map_smul'✝ } =
    (fun f => f.invFun) g
⊢ {
      toRingEquiv :=
        { toEquiv := { toFun := toFun✝, invFun := invFun✝, left_inv := left_inv✝, right_inv := right_inv✝ },
          map_mul' := map_mul'✝, map_add' := map_add'✝ },
      map_star' := map_star'✝, map_smul' := map_smul'✝ } =
    g

Next tactic:
rcases g with ⟨⟨⟨_, _, _⟩, _⟩, _⟩