-- Lean 4 proof step from Mathlib.Data.PFunctor.Multivariate.M (goal)
Goal:
n : ℕ
P : MvPFunctor.{u} (n + 1)
α : TypeVec.{u} n
R : P.M α → P.M α → Prop
h :
  ∀ (x y : P.M α),
    R x y →
      MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β := α ::: Quot R)
          (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk R)) (dest P (α := α) x) =
        MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β := α ::: Quot R)
          (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk R)) (dest P (α := α) y)
x y : P.M α
Hr : Relation.EqvGen R x y
this : ∀ (x y : P.M α), R x y → Relation.EqvGen R x y
refine_2 :
  ∀ (x y : P.M α),
    R x y →
      MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
          α ::: Quot (Relation.EqvGen R))
          (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R))) (dest P (α := α) x) =
        MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
          α ::: Quot (Relation.EqvGen R))
          (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R))) (dest P (α := α) y)
refine_2₁ :
  ∀ (x : P.M α),
    MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
        α ::: Quot (Relation.EqvGen R))
        (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R))) (dest P (α := α) x) =
      MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
        α ::: Quot (Relation.EqvGen R))
        (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R))) (dest P (α := α) x)
⊢ MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
      α ::: Quot (Relation.EqvGen R)) (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R)))
      (dest P (α := α) x) =
    MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
      α ::: Quot (Relation.EqvGen R)) (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R)))
      (dest P (α := α) y)
have refine_2₂ : ∀ (x y : P.M α),
  Relation.EqvGen R x y →
    MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
          α ::: Quot (Relation.EqvGen R))
          (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R))) (dest P (α := α) x) =
        MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
          α ::: Quot (Relation.EqvGen R))
          (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R))) (dest P (α := α) y) →
      MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
          α ::: Quot (Relation.EqvGen R))
          (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R))) (dest P (α := α) y) =
        MvFunctor.map (F := (↑P : (α : TypeVec.{u} (n + 1)) → Type u)) (α := α ::: P.M α) (β :=
          α ::: Quot (Relation.EqvGen R))
          (appendFun (α := α) (α' := α) (TypeVec.id (α := α)) (Quot.mk (Relation.EqvGen R))) (dest P (α := α) x)
Tactic: induction Hr
Cleared hypotheses: Hr