. constructor
  . simp only [l'] at l'_eq_false
    simp only [l'_eq_false, hasAssignment, ite_false] at h2
    simp only [hasAssignment, l_eq_true, getElem!, l_eq_i, i_in_bounds,
      Array.get_eq_getElem, ↓reduceIte, ↓reduceDite, h1, addAssignment, l'_eq_false,
      hasPos_of_addNeg] at h
    exact unassigned_of_has_neither _ h h2
  . intro k k_ne_zero k_ne_j_succ
    have k_eq_succ : ∃ k' : Nat, ∃ k'_succ_in_bounds : k' + 1 < (l :: acc.2.1).length, k = ⟨k' + 1, k'_succ_in_bounds⟩ := by
      have k_val_ne_zero : k.1 ≠ 0 := by
        intro k_eq_zero
        simp only [List.length_cons, ← k_eq_zero, ne_eq, not_true] at k_ne_zero
      rcases Nat.exists_eq_succ_of_ne_zero k_val_ne_zero with ⟨k', k_eq_k'_succ⟩
      rw [Nat.succ_eq_add_one k'] at k_eq_k'_succ
      have k'_succ_in_bounds : k' + 1 < (l :: acc.2.1).length := by rw [← k_eq_k'_succ]; exact k.2
      apply Exists.intro k' ∘ Exists.intro k'_succ_in_bounds
      apply Fin.eq_of_val_eq
      exact k_eq_k'_succ
    rcases k_eq_succ with ⟨k', k'_succ_in_bounds, k_eq_succ⟩
    rw [k_eq_succ]
    simp only [List.get, Nat.add_eq, Nat.add_zero, ne_eq]
    have k'_in_bounds : k' < acc.2.1.length := by
      simp only [List.length_cons, Nat.succ_eq_add_one] at k'_succ_in_bounds
      exact Nat.lt_of_succ_lt_succ k'_succ_in_bounds
    have k'_ne_j : ⟨k', k'_in_bounds⟩ ≠ j := by
      simp only [k_eq_succ, List.length_cons, Fin.mk.injEq, Nat.succ.injEq] at k_ne_j_succ
      exact Fin.ne_of_val_ne k_ne_j_succ
    exact h3 ⟨k', k'_in_bounds⟩ k'_ne_j
case right.right.right
n : Nat
f : DefaultFormula n
f_assignments_size : f.assignments.size = n
acc : Array Assignment × List (Literal (PosFin n)) × Bool × Bool
hsize : acc.fst.size = n
l : Literal (PosFin n)
ih : f.derivedLits_invariant f_assignments_size acc.fst hsize acc.snd.fst
h : ¬hasAssignment l.snd acc.fst[l.fst.val]! = true
hsize'✝ : (acc.fst.modify l.fst.val (addAssignment l.snd)).size = n :=
  Eq.mpr (id (congrArg (fun _a => _a = n) Array.modify_preserves_size)) hsize
i : Fin n
i_in_bounds : ↑i < acc.fst.size
l_in_bounds : l.fst.val < acc.fst.size
j : Fin acc.snd.fst.length
j_eq_i : (acc.snd.fst.get j).fst.val = ↑i
h1 : acc.fst[↑i] = addAssignment (acc.snd.fst.get j).snd f.assignments[↑i]
h2 : ¬hasAssignment (acc.snd.fst.get j).snd f.assignments[↑i] = true
h3 : ∀ (k : Fin acc.snd.fst.length), k ≠ j → (acc.snd.fst.get k).fst.val ≠ ↑i
l' : Literal (PosFin n) := acc.snd.fst.get j
zero_in_bounds : 0 < (l :: acc.snd.fst).length
j_succ_in_bounds : ↑j + 1 < (l :: acc.snd.fst).length
l_eq_i : l.fst.val = ↑i
l_ne_l' : true ≠ l'.snd
l_eq_true : l.snd = true
l'_eq_false : l'.snd = false
⊢ f.assignments[↑i] = unassigned ∧
    ∀ (k : Fin acc.snd.fst.length.succ),
      ¬k = ⟨0, zero_in_bounds⟩ → ¬k = ⟨↑j + 1, j_succ_in_bounds⟩ → ¬((l :: acc.snd.fst).get k).fst.val = ↑i
no goals