Module: Mathlib.Data.Ordmap.Invariants

Goal state before:
pp: α : Type u_1
l : Ordnode α
x : α
r : Ordnode α
hl : l.Balanced
hr : r.Balanced
sl : l.Sized
sr : r.Sized
⊢ l.balance x r = l.balance' x r

Tactic:
obtain - | ⟨ls, ll, lx, lr⟩ := l
  · obtain - | ⟨rs, rl, rx, rr⟩ := r
    · rfl
    · rw [sr.eq_node'] at hr ⊢
      obtain - | ⟨rls, rll, rlx, rlr⟩ := rl <;> obtain - | ⟨rrs, rrl, rrx, rrr⟩ := rr <;>
        dsimp +instances [balance, balance']
      · rfl
      · have : size rrl = 0 ∧ size rrr = 0 := by
          have := balancedSz_zero.1 hr.1.symm
          rwa [size, sr.2.2.1, Nat.succ_le_succ_iff, Nat.le_zero, add_eq_zero] at this
        cases sr.2.2.2.1.size_eq_zero.1 this.1
        cases sr.2.2.2.2.size_eq_zero.1 this.2
        obtain rfl : rrs = 1 := sr.2.2.1
        rw [if_neg, rotateL_node, if_pos]; · rfl
        all_goals (try dsimp only [size]); decide
      · have : size rll = 0 ∧ size rlr = 0 := by
          have := balancedSz_zero.1 hr.1
          rwa [size, sr.2.1.1, Nat.succ_le_succ_iff, Nat.le_zero, add_eq_zero] at this
        cases sr.2.1.2.1.size_eq_zero.1 this.1
        cases sr.2.1.2.2.size_eq_zero.1 this.2
        obtain rfl : rls = 1 := sr.2.1.1
        rw [if_neg, rotateL_node, if_neg]; · rfl
        all_goals (try dsimp only [size]); decide
      · symm; rw [zero_add, if_neg, rotateL]
        · dsimp only [size_node]; split_ifs
          · simp [node3L, node']; abel
          · simp [node4L, node', sr.2.1.1]; abel
        · exact not_le_of_gt (Nat.succ_lt_succ (add_pos sr.2.1.pos sr.2.2.pos))
  · obtain - | ⟨rs, rl, rx, rr⟩ := r
    · rw [sl.eq_node'] at hl ⊢
      obtain - | ⟨lls, lll, llx, llr⟩ := ll <;> obtain - | ⟨lrs, lrl, lrx, lrr⟩ := lr <;>
        dsimp [balance, balance']
      · rfl
      · have : size lrl = 0 ∧ size lrr = 0 := by
          have := balancedSz_zero.1 hl.1.symm
          rwa [size, sl.2.2.1, Nat.succ_le_succ_iff, Nat.le_zero, add_eq_zero] at this
        cases sl.2.2.2.1.size_eq_zero.1 this.1
        cases sl.2.2.2.2.size_eq_zero.1 this.2
        obtain rfl : lrs = 1 := sl.2.2.1
        rw [if_neg, rotateR_node, if_neg]; · rfl
        all_goals (try dsimp only [size]); decide
      · have : size lll = 0 ∧ size llr = 0 := by
          have := balancedSz_zero.1 hl.1
          rwa [size, sl.2.1.1, Nat.succ_le_succ_iff, Nat.le_zero, add_eq_zero] at this
        cases sl.2.1.2.1.size_eq_zero.1 this.1
        cases sl.2.1.2.2.size_eq_zero.1 this.2
        obtain rfl : lls = 1 := sl.2.1.1
        rw [if_neg, rotateR_node, if_pos]; · rfl
        all_goals (try dsimp only [size]); decide
      · symm; rw [if_neg, rotateR]
        · dsimp only [size_node]; split_ifs
          · simp [node3R, node']; abel
          · simp [node4R, node', sl.2.2.1]; abel
        · exact not_le_of_gt (Nat.succ_lt_succ (add_pos sl.2.1.pos sl.2.2.pos))
    · simp only [balance, id_eq, balance', size_node, gt_iff_lt]
      symm; rw [if_neg]
      · split_ifs with h h_1
        · have rd : delta ≤ size rl + size rr := by
            have := lt_of_le_of_lt (Nat.mul_le_mul_left _ sl.pos) h
            rwa [sr.1, Nat.lt_succ_iff] at this
          obtain - | ⟨rls, rll, rlx, rlr⟩ := rl
          · rw [size, zero_add] at rd
            exact absurd (le_trans rd (balancedSz_zero.1 hr.1.symm)) (by decide)
          obtain - | ⟨rrs, rrl, rrx, rrr⟩ := rr
          · exact absurd (le_trans rd (balancedSz_zero.1 hr.1)) (by decide)
          dsimp [rotateL]; split_ifs
          · simp [node3L, node', sr.1]; abel
          · simp [node4L, node', sr.1, sr.2.1.1]; abel
        · have ld : delta ≤ size ll + size lr := by
            have := lt_of_le_of_lt (Nat.mul_le_mul_left _ sr.pos) h_1
            rwa [sl.1, Nat.lt_succ_iff] at this
          obtain - | ⟨lls, lll, llx, llr⟩ := ll
          · rw [size, zero_add] at ld
            exact absurd (le_trans ld (balancedSz_zero.1 hl.1.symm)) (by decide)
          obtain - | ⟨lrs, lrl, lrx, lrr⟩ := lr
          · exact absurd (le_trans ld (balancedSz_zero.1 hl.1)) (by decide)
          dsimp [rotateR]; split_ifs
          · simp [node3R, node', sl.1]; abel
          · simp [node4R, node', sl.1, sl.2.2.1]; abel
        · simp [node']
      · exact not_le_of_gt (add_le_add (Nat.succ_le_of_lt sl.pos) (Nat.succ_le_of_lt sr.pos))

Goal state after: