-- Mathlib/Data/Ordmap/Ordset.lean
theorem Valid'.erase_aux [DecidableRel (α := α) (· ≤ ·)] (x : α) {t a₁ a₂} (h : Valid' a₁ t a₂) :
    Valid' a₁ (erase x t) a₂ ∧ Raised (erase x t).size t.size

Proof state:
case node.intro.intro.gt
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
⊢ (∃ l', Raised l' t_l.size ∧ BalancedSz l' (erase x t_r).size) ∨
    ∃ r', Raised (erase x t_r).size r' ∧ BalancedSz t_l.size r'

Tactic:
right

Result:
case node.intro.intro.gt.h
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
⊢ ∃ r', Raised (erase x t_r).size r' ∧ BalancedSz t_l.size r'

Proof state:
case node.intro.intro.lt.h
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
⊢ ∃ l', Raised (erase x t_l).size l' ∧ BalancedSz l' t_r.size

Tactic:
exists t_l.size

Result:
case node.intro.intro.lt.h
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
⊢ Raised (erase x t_l).size t_l.size ∧ BalancedSz t_l.size t_r.size

Proof state:
case node.intro.intro
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
⊢ Valid' a₁
      (match cmpLE x t_x with
      | Ordering.lt => (erase x t_l).balanceR t_x t_r
      | Ordering.eq => t_l.glue t_r
      | Ordering.gt => t_l.balanceL t_x (erase x t_r))
      a₂ ∧
    Raised
      (match cmpLE x t_x with
        | Ordering.lt => (erase x t_l).balanceR t_x t_r
        | Ordering.eq => t_l.glue t_r
        | Ordering.gt => t_l.balanceL t_x (erase x t_r)).size
      size✝

Tactic:
cases cmpLE x t_x <;> rw [h.sz.1]

Result:
case node.intro.intro.lt
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
⊢ Valid' a₁
      (match Ordering.lt with
      | Ordering.lt => (erase x t_l).balanceR t_x t_r
      | Ordering.eq => t_l.glue t_r
      | Ordering.gt => t_l.balanceL t_x (erase x t_r))
      a₂ ∧
    Raised
      (match Ordering.lt with
        | Ordering.lt => (erase x t_l).balanceR t_x t_r
        | Ordering.eq => t_l.glue t_r
        | Ordering.gt => t_l.balanceL t_x (erase x t_r)).size
      (t_l.size + t_r.size + 1)

case node.intro.intro.eq
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
⊢ Valid' a₁
      (match Ordering.eq with
      | Ordering.lt => (erase x t_l).balanceR t_x t_r
      | Ordering.eq => t_l.glue t_r
      | Ordering.gt => t_l.balanceL t_x (erase x t_r))
      a₂ ∧
    Raised
      (match Ordering.eq with
        | Ordering.lt => (erase x t_l).balanceR t_x t_r
        | Ordering.eq => t_l.glue t_r
        | Ordering.gt => t_l.balanceL t_x (erase x t_r)).size
      (t_l.size + t_r.size + 1)

case node.intro.intro.gt
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
⊢ Valid' a₁
      (match Ordering.gt with
      | Ordering.lt => (erase x t_l).balanceR t_x t_r
      | Ordering.eq => t_l.glue t_r
      | Ordering.gt => t_l.balanceL t_x (erase x t_r))
      a₂ ∧
    Raised
      (match Ordering.gt with
        | Ordering.lt => (erase x t_l).balanceR t_x t_r
        | Ordering.eq => t_l.glue t_r
        | Ordering.gt => t_l.balanceL t_x (erase x t_r)).size
      (t_l.size + t_r.size + 1)

Proof state:
case node.intro.intro.eq
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
h_glue : Valid' a₁ (t_l.glue t_r) a₂ ∧ (t_l.glue t_r).size = t_l.size + t_r.size
⊢ Valid' a₁
      (match Ordering.eq with
      | Ordering.lt => (erase x t_l).balanceR t_x t_r
      | Ordering.eq => t_l.glue t_r
      | Ordering.gt => t_l.balanceL t_x (erase x t_r))
      a₂ ∧
    Raised
      (match Ordering.eq with
        | Ordering.lt => (erase x t_l).balanceR t_x t_r
        | Ordering.eq => t_l.glue t_r
        | Ordering.gt => t_l.balanceL t_x (erase x t_r)).size
      (t_l.size + t_r.size + 1)

Tactic:
obtain ⟨h_glue_valid, h_glue_sized⟩ := h_glue

Result:
case node.intro.intro.eq.intro
α : Type u_1
inst✝¹ : Preorder α
inst✝ : DecidableRel fun x1 x2 => x1 ≤ x2
x : α
size✝ : ℕ
t_l : Ordnode α
t_x : α
t_r : Ordnode α
a₁ : WithBot α
a₂ : WithTop α
h : Valid' a₁ (Ordnode.node size✝ t_l t_x t_r) a₂
t_l_valid : Valid' a₁ (erase x t_l) ↑t_x
t_l_size : Raised (erase x t_l).size t_l.size
t_r_valid : Valid' (↑t_x) (erase x t_r) a₂
t_r_size : Raised (erase x t_r).size t_r.size
h_glue_valid : Valid' a₁ (t_l.glue t_r) a₂
h_glue_sized : (t_l.glue t_r).size = t_l.size + t_r.size
⊢ Valid' a₁
      (match Ordering.eq with
      | Ordering.lt => (erase x t_l).balanceR t_x t_r
      | Ordering.eq => t_l.glue t_r
      | Ordering.gt => t_l.balanceL t_x (erase x t_r))
      a₂ ∧
    Raised
      (match Ordering.eq with
        | Ordering.lt => (erase x t_l).balanceR t_x t_r
        | Ordering.eq => t_l.glue t_r
        | Ordering.gt => t_l.balanceL t_x (erase x t_r)).size
      (t_l.size + t_r.size + 1)