. constructor
  . simp only [Fin.getElem_fin]
    exact ih1
  . constructor
    . simp only [Fin.getElem_fin]
      exact ih2
    . constructor
      . simp only [clearUnit, Array.get_eq_getElem]
        have idx_res_ne_i : units[idx.1].1.1 ≠ i.1 := by
          intro h1
          by_cases units[idx.1].2
          . next h2 =>
            have h3 := units_nodup idx j1 idx_ne_j1
            simp only [Fin.getElem_fin, ih1, ← h1, ← h2, ne_eq] at h3
            exact h3 rfl
          . next h2 =>
            have h3 := units_nodup idx j2 idx_ne_j2
            simp only [Bool.not_eq_true] at h2
            simp only [Fin.getElem_fin, ih2, ← h1, ← h2, ne_eq] at h3
            exact h3 rfl
        have idx_unit_in_bounds : units[idx.1].1.1 < assignments.size := by
          rw [hsize]; exact units[idx.1].1.2.2
        have i_in_bounds : i.1 < assignments.size := hsize ▸ i.2
        rw [Array.get_modify_unchanged idx_unit_in_bounds i_in_bounds _ idx_res_ne_i]
        exact ih3
      . constructor
        . exact ih4
        . intro k k_ge_idx_add_one
          exact ih5 k $ Nat.le_of_succ_le k_ge_idx_add_one
case right.right
n : Nat
f : DefaultFormula n
f_assignments_size : f.assignments.size = n
units : Array (Literal (PosFin n))
units_nodup : ∀ (i j : Fin units.size), i ≠ j → units[i] ≠ units[j]
idx : Fin units.size
assignments : Array Assignment
hsize : assignments.size = n
hsize' : (clearUnit assignments units[idx]).size = n
i : Fin n
j1 : Fin units.size
j1_ge_idx : ↑j1 ≥ ↑idx
j2 : Fin units.size
j2_ge_idx : ↑j2 ≥ ↑idx
i_gt_zero : ↑i > 0
ih1 : units[↑j1] = (⟨↑i, ⋯⟩, true)
ih2 : units[↑j2] = (⟨↑i, ⋯⟩, false)
ih3 : assignments[↑i] = both
ih4 : f.assignments[↑i] = unassigned
ih5 : ∀ (k : Fin units.size), ↑k ≥ ↑idx → ¬k = j1 → ¬k = j2 → ¬units[↑k].fst.val = ↑i
idx_ne_j1 : ¬idx = j1
idx_ne_j2 : ¬idx = j2
⊢ units[j1] = (⟨↑i, ⋯⟩, true) ∧
    units[j2] = (⟨↑i, ⋯⟩, false) ∧
      (clearUnit assignments units[idx])[↑i] = both ∧
        f.assignments[↑i] = unassigned ∧ ∀ (k : Fin units.size), ↑k ≥ ↑idx + 1 → k ≠ j1 → k ≠ j2 → units[k].fst.val ≠ ↑i
no goals